CHAPTER IV.

THE CIRCUMNUTATING MOVEMENTS OF THE SEVERAL PARTS OF MATURE PLANTS.

Circumnutation of stems: concluding remarks on—Circumnutation of

stolons: aid thus afforded in winding amongst the stems of surrounding

plants—Circumnutation of flower-stems—Circumnutation of Dicotyledonous

leaves—Singular oscillatory movement of leaves of Dionaea—Leaves of

Cannabis sink at night—Leaves of Gymnosperms—Of

Monocotyledons—Cryptogams—Concluding remarks on the circumnutation of

leaves; generally rise in the evening and sink in the morning.

We have seen in the first chapter that the stems of all seedlings,

whether hypocotyls or epicotyls, as well as the cotyledons and the

radicles, are continually circumnutating—that is they grow first on one

side and then on another, such growth being probably preceded by

increased turgescence of the cells. As it was unlikely that plants

should change their manner of growth with advancing age, it seemed

probable that the various organs of all plants at all ages, as long as

they continued to grow, would be found to circumnutate, though perhaps

to an extremely small extent. As it was important for us to discover

whether this was the case, we determined to observe carefully a certain

number of plants which were growing vigorously, and which were not

known to move in any manner. We commenced with stems. Observations of

this kind are tedious, and it appeared to us that it would be

sufficient to observe the stems in about a score of genera, belonging

to widely distinct families and inhabitants of various countries.

Several plants

were selected which, from being woody, or for other reasons, seemed the

least likely to circumnutate. The observations and the diagrams were

made in the manner described in the Introduction. Plants in pots were

subjected to a proper temperature, and whilst being observed, were kept

either in darkness or were feebly illuminated from above. They are

arranged in the order adopted by Hooker in Le Maout and Decaisne’s

‘System of Botany.’ The number of the family to which each genus

belongs is appended, as this serves to show the place of each in the

series.

(1.) Iberis umbellata (Cruciferae, Fam. 14).—The movement of the stem

of a young plant, 4 inches in height, consisting of four internodes

(the hypocotyl included) besides a large bud on the summit, was traced,

as here shown, during 24 h. (Fig. 70). As far as we could judge the

uppermost inch alone of the stem circumnutated, and this in a simple

manner. The movement was slow, and the rate very unequal at different

times. In part of its course an irregular ellipse, or rather triangle,

was completed in 6 h. 30 m.

Fig. 70. Iberis umbellata: circumnutation of stem of young plant,

traced from 8.30 A.M. Sept. 13th to same hour on following morning.

Distance of summit of stem beneath the horizontal glass 7.6 inches.

Diagram reduced to half of original size. Movement as here shown

magnified between 4 and 5 times.

(2.) Brassica oleracea (Cruciferae).—A very young plant, bearing three

leaves, of which the longest was only three-quarters of an inch in

length, was placed under a microscope, furnished with an eye-piece

micrometer, and the tip of the largest leaf was

found to be in constant movement. It crossed five divisions of the

micrometer, that is, 1/100th of an inch, in 6 m. 20 s. There could

hardly be a doubt that it was the stem which chiefly moved, for the tip

did not get quickly out of focus; and this would have occurred had the

movement been confined to the leaf, which moves up or down in nearly

the same vertical plane.

(3.) Linum usitatissimum (Lineae, Fam. 39).—The stems of this plant,

shortly before the flowering period, are stated by Fritz Müller

(‘Jenaische Zeitschrift,’ B. v. p. 137) to revolve, or circumnutate.

(4.) Pelargonium zonale (Geraniaceae, Fam. 47).—A young plant, 7½

inches in height, was observed in the usual manner; but, in order to

see the bead at the end of the glass filament and at the same time the

mark beneath, it was necessary to cut off three leaves on one side. We

do not know whether it was owing to this cause, or to the plant having

previously become bent to one side through heliotropism, but from the

morning of the 7th of March to 10.30 P.M. on the 8th, the stem moved a

considerable distance in a zigzag line in the same general direction.

During the night of the 8th it moved to some distance at right angles

to its former course, and next morning (9th) stood for a time almost

still. At noon on the 9th a new tracing was begun (see Fig. 71), which

was continued till 8 A.M. on the 11th. Between noon on the 9th and 5

P.M. on the 10th (i.e. in the course of 29 h.), the stem described a

circle. This plant therefore circumnutates, but at a very slow rate,

and to a small extent.

Fig. 71. Pelargonium zonale: circumnutation of stem of young plant,

feebly illuminated from above. Movement of bead magnified about 11

times; traced on a horizontal glass from noon on March 9th to 8 A.M. on

the 11th.

(5.) Tropaeolum majus (?) (dwarfed var. called Tom Thumb);

(Geraniaceae, Fam. 47).—The species of this genus climb by the

aid of their sensitive petioles, but some of them also twine round

supports; but even these latter species do not begin to circumnutate in

a conspicuous manner whilst young. The variety here treated of has a

rather thick stem, and is so dwarf that apparently it does not climb in

any manner. We therefore wished to ascertain whether the stem of a

young plant, consisting of two internodes, together 3.2 inches in

height, circumnutated. It was observed during 25 h., and we see in Fig.

72 that the stem moved in a zigzag course, indicating circumnutation.

Fig. 72. Tropaeolum majus (?): circumnutation of stem of young plant,

traced on a horizontal glass from 9 A.M. Dec. 26th to 10 A.M. on 27th.

Movement of bead magnified about 5 times, and here reduced to half of

original scale.

Fig. 73. Trifolium resupinatum: circumnutation of stem, traced on

vertical glass from 9.30 A.M. to 4.30 P.M. Nov. 3rd. Tracing not

greatly magnified, reduced to half of original size. Plant feebly

illuminated from above.

(6.) Trifolium resupinatum (Leguminosae, Fam. 75).—When we treat of the

sleep of plants, we shall see that the stems in several Leguminous

genera, for instance, those of Hedysarum, Mimosa, Melilotus, etc.,

which are not climbers, circumnutate in a conspicuous manner. We will

here give only a single instance (Fig. 73), showing the circumnutation

of the stem of a large plant of a clover, Trifolium resupinatum. In the

course of 7 h. the stem changed

its course greatly eight times and completed three irregular circles or

ellipses. It therefore circumnutated rapidly. Some of the lines run at

right angles to one another.

Fig. 74. Rubus (hybrid): circumnutation of stem, traced on horizontal

glass, from 4 P.M. March 14th to 8.30 A.M. 16th. Tracing much

magnified, reduced to half of original size. Plant illuminated feebly

from above.

(7.) Rubus idæus (hybrid) (Rosaceae, Fam. 76).—As we happened to have a

young plant, 11 inches in height and growing vigorously, which had been

raised from a cross between the raspberry (Rubus idæus) and a North

American Rubus, it was observed in the usual manner. During the morning

of March 14th the stem almost completed a circle, and then moved far to

the right. At 4 P.M. it reversed its course, and now a fresh tracing

was begun, which was continued during 40½ h., and is given in Fig. 74.

We here have well-marked circumnutation.

(8.) Deutzia gracilis (Saxifrageae, Fam. 77).—A shoot on a bush about

18 inches in height was observed. The bead changed its course greatly

eleven times in the course of 10 h. 30 m. (Fig. 75), and there could be

no doubt about the circumnutation of the stem.

Fig. 75. Deutzia gracilis: circumnutation of stem, kept in darkness,

traced on horizontal glass, from 8.30 A.M. to 7 P.M. March 20th.

Movement of bead originally magnified about 20 times, here reduced to

half scale.

(9.) Fuchsia (greenhouse var., with large flowers, probably a hybrid)

(Onagrarieae, Fam. 100).—A young plant, 15 inches in height, was

observed during nearly 48 h. The

accompanying figure (Fig. 76) gives the necessary particulars, and

shows that the stem circumnutated, though rather slowly.

Fig. 76. Fuchsia (garden var.): circumnutation of stem, kept in

darkness, traced on horizontal glass, from 8.30 A.M. to 7 P.M. March

20th. Movement of bead originally magnified about 40 times, here

reduced to half scale.

(10.) Cereus speciocissimus (garden var., sometimes called Phyllocactus

multiflorus) (Cacteæ, Fam. 109).—This plant, which was growing

vigorously from having been removed a few days before from the

greenhouse to the hot-house, was observed with especial interest, as it

seemed so little probable that the stem would circumnutate. The

branches are flat, or flabelliform; but some of them are triangular in

section, with the three sides hollowed out. A branch of this latter

shape, 9 inches in length and 1½ in diameter, was chosen for

observation, as less likely to circumnutate than a flabelliform branch.

The movement of the bead at the end of the glass filament, affixed to

the summit of the branch, was traced (A, Fig. 77) from 9.23 A.M. to

4.30 P.M. on Nov. 23rd, during which time it changed its course greatly

six times. On the 24th another tracing was made (see B), and the bead

on this day changed its course oftener, making in 8 h. what may be

considered as four ellipses, with their longer axes differently

directed. The position of the stem and its commencing course on the

following morning are likewise shown. There can be no doubt that this

branch, though appearing quite rigid, circumnutated; but the

extreme amount of movement during the time was very small, probably

rather less than the 1/20th of an inch.

Fig 77. Cereus speciocissimus: circumnutation of stem, illuminated from

above, traced on a horizontal glass, in A from 9 A.M. to 4.30 P.M. on

Nov. 23rd; and in B from 8.30 A.M. on the 24th to 8 A.M. on the 25th.

Movement of the bead in B magnified about 38 times.

(11.) Hedera helix (Araliaceae, Fam. 114).—The stem is known to be

apheliotropic, and several seedlings growing in a pot in the greenhouse

became bent in the middle of the summer at right angles from the light.

On Sept. 2nd some of these stems were tied up so as to stand

vertically, and were placed before a north-east window; but to our

surprise they were now decidedly heliotropic, for during 4 days they

curved themselves towards the light, and their course being traced on a

horizontal glass, was strongly zigzag. During the 6 succeeding days

they circumnutated over the same small space at a slow rate, but there

could be no doubt about their circumnutation. The plants were kept

exactly in the same place before the window, and after an interval of

15 days the stems were again observed during 2 days and their movements

traced, and

they were found to be still circumnutating, but on a yet smaller scale.

(12.) Gazania ringens (Compositæ, Fam. 122).—The circumnutation of the

stem of a young plant, 7 inches in height, as measured to the tip of

the highest leaf, was traced during 33 h., and is shown in the

accompanying figure (Fig. 78). Two main lines may be observed running

at nearly right angles to two other main lines; but these are

interrupted by small loops.

Fig. 78. Gazania ringens: circumnutation of stem traced from 9 A.M.

March 21st to 6 P.M. on 22nd; plant kept in darkness. Movement of bead

at the close of the observations magnified 34 times, here reduced to

half the original scale.

(13.) Azalea Indica (Ericineae, Fam. 128).—A bush 21 inches in height

was selected for observation, and the circumnutation of its leading

shoot was traced during 26 h. 40 m., as shown in the following figure

(Fig. 79).

(14.) Plumbago Capensis (Plumbagineae, Fam. 134).—A small lateral

branch which projected from a tall freely growing bush, at an angle of

35° above the horizon, was selected for observation. For the first 11

h. it moved to a considerable distance in a nearly straight line to one

side, owing probably to its having been previously deflected by the

light whilst standing in the greenhouse. At 7.20 P.M. on March 7th a

fresh tracing was begun and continued for the next 43 h. 40 m. (see

Fig. 80). During the first 2 h. it followed nearly the same direction

as before, and then changed it a little; during the night it moved at

nearly right angles to its previous course. Next

day (8th) it zigzagged greatly, and on the 9th moved irregularly round

and round a small circular space. By 3 P.M. on the 9th the figure had

become so complicated that no more dots could be made; but the shoot

continued during the evening of the 9th, the whole of the 10th, and the

morning of the 11th to circumnutate over the same small space, which

was only about the 1/26th of an inch (.97 mm.) in diameter. Although

this branch circumnutated to a very small extent, yet it changed its

course frequently. The movements ought to have been more magnified.

Fig. 79. Azalea Indica: circumnutation of stem, illuminated from above,

traced on horizontal glass, from 9.30 A.M. March 9th to 12.10 P.M. on

the 10th. But on the morning of the 10th only four dots were made

between 8.30 A.M. and 12.10 P.M., both hours included, so that the

circumnutation is not fairly represented in this part of the diagram.

Movement of the bead here magnified about 30 times.

Fig. 80. Plumbago Capensis: circumnutation of tip of a lateral branch,

traced on horizontal glass, from 7.20 P.M. on March 7th to 3 P.M. on

the 9th. Movement of bead magnified 13 times. Plant feebly illuminated

from above.

(15.) Aloysia citriodora (Verbenaceae, Fam. 173).—The following figure

(Fig. 81) gives the movements of a shoot during

31 h. 40 m., and shows that it circumnutated. The bush was 15 inches in

height.

Fig. 81. Aloysia citriodora: circumnutation of stem, traced from 8.20

A.M. on March 22nd to 4 P.M. on 23rd. Plant kept in darkness. Movement

magnified about 40 times.

(16.) Verbena melindres (?) (a scarlet-flowered herbaceous var.)

(Verbenaceae).—A shoot 8 inches in height had been laid horizontally,

for the sake of observing its apogeotropism, and the terminal portion

had grown vertically upwards for a length of 1½ inch. A glass filament,

with a bead at the end, was fixed upright to the tip, and its movements

were traced during 41 h. 30 m. on a vertical glass (Fig. 82). Under

these circumstances the lateral movements were chiefly shown; but as

the lines from side to side are not on the same level, the shoot

must have moved in a plane at right angles to that of the lateral

movement, that is, it must have circumnutated. On the next day (6th)

the shoot moved in the course of 16 h. four times to the right, and

four times to the left; and this apparently represents the formation of

four ellipses, so that each was completed in 4 h. (17.) Ceratophyllum

demersum (Ceratophylleae, Fam. 220).—An interesting account of the

movements of the stem of this water-plant has been published by M. E.

Rodier.[1] The movements are confined to the young internodes, becoming

less and less lower down the stem; and they are extraordinary from

their amplitude. The stems sometimes moved through an angle of above

200° in 6 h., and in one instance through 220° in 3 h. They generally

bent from right to left in the morning, and in an opposite direction in

the afternoon; but the movement was sometimes temporarily reversed or

quite arrested. It was not affected by light. It does not appear that

M. Rodier made any diagram on a horizontal plane representing the

actual course pursued by the apex, but he speaks of the “branches

executing round their axes of growth a movement of torsion.” From the

particulars above given, and remembering in the case of twining plants

and of tendrils, how difficult it is not to mistake their bending to

all points of the compass for true torsion, we are led to believe that

the stems of this Ceratophyllum circumnutate, probably in the shape of

narrow ellipses, each completed in about 26 h. The following statement,

however, seems to indicate something different from ordinary

circumnutation, but we cannot fully understand it. M. Rodier says: “Il

est alors facile de voir que le mouvement de flexion se produit d’abord

dans les mérithalles supérieurs, qu’il se propage ensuite, en

s’amoindrissant du haut en bas; tandis qu’au contraire le movement de

redressement commence par la partie inférieur pour se terminer a la

partie supérieure qui, quelquefois, peu de temps avant de se relever

tout à fait, forme avec l’axe un angle très aigu.”

[1] ‘Comptes Rendus,’ April 30th, 1877. Also a second notice published

separately in Bourdeaux, Nov. 12th, 1877.

Fig. 82. Verbena melindres: circumnutation of stem in darkness, traced

on vertical glass, from 5.30 P.M. on June 5th to 11 A.M. June 7th.

Movement of bead magnified 9 times.

(18.) Coniferæ.—Dr. Maxwell Masters states (‘Journal Linn. Soc.,’ Dec.

2nd, 1879) that the leading shoots of many Coniferæ during the season

of their active growth exhibit very remarkable movements of revolving

nutation, that is, they circumnutate. We may feel sure that the lateral

shoots whilst growing would exhibit the same movement if carefully

observed.

(19.) Lilium auratum (Fam. Liliaceae).—The circumnutation of the stem

of a plant 24 inches in height is represented in the above figure (Fig.

83).

Fig. 83. Lilium auratum: circumnutation of a stem in darkness, traced

on a horizontal glass, from 8 A.M. on March 14th to 8.35 A.M. on 16th.

But it should be noted that our observations were interrupted between 6

P.M. on the 14th and 12.15 P.M. on the 15th, and the movements during

this interval of 18 h. 15 m. are represented by a long broken line.

Diagram reduced to half original scale.

Fig. 84. Cyperus alternifolius: circumnutation of stem, illuminated

from above, traced on horizontal glass, from 9.45 A.M. March 9th to 9

P.M. on 10th. The stem grew so rapidly whilst being observed, that it

was not possible to estimate how much its movements were magnified in

the tracing.

(20.) Cyperus alternifolius (Fam. Cyperaceae.)—A glass

filament, with a bead at the end, was fixed across the summit of a

young stem 10 inches in height, close beneath the crown of elongated

leaves. On March 8th, between 12.20 and 7.20 P.M. the stem described an

ellipse, open at one end. On the following day a new tracing was begun

(Fig. 84), which plainly shows that the stem completed three irregular

figures in the course of 35 h. 15 m.

Concluding Remarks on the Circumnutation of Stems.—Any one who will

inspect the diagrams now given, and will bear in mind the widely

separated position of the plants described in the series,—remembering

that we have good grounds for the belief that the hypocotyls and

epicotyls of all seedlings circumnutate,—not forgetting the number of

plants distributed in the most distinct families which climb by a

similar movement,—will probably admit that the growing stems of all

plants, if carefully observed, would be found to circumnutate to a

greater or less extent. When we treat of the sleep and other movements

of plants, many other cases of circumnutating stems will be

incidentally given. In looking at the diagrams, we should remember that

the stems were always growing, so that in each case the circumnutating

apex as it rose will have described a spire of some kind. The dots were

made on the glasses generally at intervals of an hour, or hour and a

half, and were then joined by straight lines. If they had been made at

intervals of 2 or 3 minutes, the lines would have been more

curvilinear, as in the case of the tracks left on the smoked

glass-plates by the tips of the circumnutating radicles of seedling

plants. The diagrams generally approach in form to a succession of more

or less irregular ellipses or ovals, with their longer axes directed to

different points of the compass during the same day or on succeeding

days. The stems

therefore, sooner or later, bend to all sides; but after a stem has

bent in any one direction, it commonly bends back at first in nearly,

though not quite, the opposite direction; and this gives the tendency

to the formation of ellipses, which are generally narrow, but not so

narrow as those described by stolons and leaves. On the other hand, the

figures sometimes approach in shape to circles. Whatever the figure may

be, the course pursued is often interrupted by zigzags, small

triangles, loops, or ellipses. A stem may describe a single large

ellipse one day, and two on the next. With different plants the

complexity, rate, and amount of movement differ much. The stems, for

instance, of Iberis and Azalea described only a single large ellipse in

24 h.; whereas those of the Deutzia made four or five deep zigzags or

narrow ellipses in 11½ h., and those of the Trifolium three triangular

or quadrilateral figures in 7 h.

CIRCUMNUTATION OF STOLONS OR RUNNERS.

Stolons consist of much elongated, flexible branches, which run along

the surface of the ground and form roots at a distance from the

parent-plant. They are therefore of the same homological nature as

stems; and the three following cases may be added to the twenty

previously given cases.

Fragaria (cultivated garden var.): Rosaceae.—A plant growing in a pot

had emitted a long stolon; this was supported by a stick, so that it

projected for the length of several inches horizontally. A glass

filament bearing two minute triangles of paper was affixed to the

terminal bud, which was a little upturned; and its movements were

traced during 21 h., as shown in Fig. 85. In the course of the first 12

h. it moved twice up and twice down in somewhat zigzag lines, and no

doubt travelled in the same manner during the night. On the following

morning after an interval of 20 h. the apex stood a little higher than

it did at first, and this shows that the stolon had not been acted on

within this time by geotropism;[2] nor had its own weight caused it to

bend downwards.

[2] Dr. A. B. Frank states (‘Die Naturliche wagerechte Richtung von

Pflanzentheilen,’ 1870, p. 20) that the stolons of this plant are

acted on by geotropism, but only after a considerable interval of

time.

Fig. 85. Fragaria: circumnutation of stolon, kept in darkness, traced

on vertical glass, from 10.45 A.M. May 18th to 7.45 A.M. on 19th.

On the following morning (19th) the glass filament was detached and

refixed close behind the bud, as it appeared possible that the

circumnutation of the terminal bud and of the adjoining part of the

stolon might be different. The movement was now traced during two

consecutive days (Fig. 86). During the first day the filament travelled

in the course of 14 h. 30 m. five times up and four times down, besides

some lateral movement. On the 20th the course was even more

complicated, and can hardly be followed in the figure; but the filament

moved in 16 h. at least five times up and five times down, with very

little

lateral deflection. The first and last dots made on this second day,

viz., at 7 A.M. and 11 P.M., were close together, showing that the

stolon had not fallen or risen. Nevertheless, by comparing its position

on the morning of the 19th and 21st, it is obvious that the stolon had

sunk; and this may be attributed to slow bending down either from its

own weight or from geotropism.

Fig. 86. Fragaria: circumnutation of the same stolon as in the last

figure, observed in the same manner, and traced from 8 A.M. May 19th to

8 A.M. 21st.

During a part of the 20th an orthogonal tracing was made by applying a

cube of wood to the vertical glass and bringing the apex of the stolon

at successive periods into a line with one edge; a dot being made each

time on the glass. This tracing therefore represented very nearly the

actual amount of movement of the apex; and in the course of 9 h. the

distance of the extreme dots from one another was .45 inch. By the same

method it was ascertained that the apex moved between 7 A.M. on the

20th and 8 A.M. on the 21st a distance of .82 inch.

A younger and shorter stolon was supported so that it projected at

about 45° above the horizon, and its movement was traced by the same

orthogonal method. On the first day the apex soon rose above the field

of vision. By the next morning it had sunk, and the course pursued was

now traced during 14 h. 30 m. (Fig. 87). The amount of movement was

almost the same,

from side to side as up and down; and differed in this respect

remarkably from the movement in the previous cases. During the latter

part of the day, viz., between 3 and 10.30 P.M., the actual distance

travelled by the apex amounted to 1.15 inch; and in the course of the

whole day to at least 2.67 inches. This is an amount of movement almost

comparable with that of some climbing plants. The same stolon was

observed on the following day, and now it moved in a somewhat less

complex manner, in a plane not far from vertical. The extreme amount of

actual movement was 1.55 inch in one direction, and .6 inch in another

direction at right angles. During neither of these days did the stolon

bend downwards through geotropism or its own weight.

Fig. 87. Fragaria: circumnutation of another and younger stolon, traced

from 8 A.M. to 10.30 P.M. Figure reduced to one-half of original scale.

Four stolons still attached to the plant were laid on damp sand in the

back of a room, with their tips facing the north-east windows. They

were thus placed because De Vries says[3] that they are apheliotropic

when exposed to the light of the sun; but we could not perceive any

effect from the above feeble degree of illumination. We may add that on

another occasion, late in the summer, some stolons, placed upright

before a south-west window

on a cloudy day, became distinctly curved towards the light, and were

therefore heliotropic. Close in front of the tips of the prostrate

stolons, a crowd of very thin sticks and the dried haulms of grasses

were driven into the sand, to represent the crowded stems of

surrounding plants in a state of nature. This was done for the sake of

observing how the growing stolons would pass through them. They did so

easily in the course of 6 days, and their circumnutation apparently

facilitated their passage. When the tips encountered sticks so close

together that they could not pass between them, they rose up and passed

over them. The sticks and haulms were removed after the passage of the

four stolons, two of which were found to have assumed a permanently

sinuous shape, and two were still straight. But to this subject we

shall recur under Saxifraga.

[3] ‘Arbeiten Bot Inst., Würzburg,’ 1872, p. 434.

Saxifraga sarmentosa (Saxifrageae).—A plant in a suspended pot had

emitted long branched stolons, which depended like threads on all

sides. Two were tied up so as to stand vertically, and their upper ends

became gradually bent downwards, but so slowly in the course of several

days, that the bending was probably due to their weight and not to

geotropism. A glass filament with little triangles of paper was fixed

to the end of one of these stolons, which was 17½ inches in length, and

had already become much bent down, but still projected at a

considerable angle above the horizon. It moved only slightly three

times from side to side and then upwards; on the following day

the movement was even less. As this stolon was so long we thought that

its growth was nearly completed, so we tried another which was thicker

and shorter, viz., 10 1/4 inches in length. It moved greatly, chiefly

upwards, and changed its course five times in the course of the day.

During the night it curved so much upwards in opposition to gravity,

that the movement could no longer be traced on the vertical glass, and

a horizontal one had to be used. The movement was followed during the

next 25 h., as shown in Fig. 88. Three irregular ellipses, with their

longer axes somewhat differently directed, were almost completed in the

first 15 h. The extreme actual amount of movement of the tip during the

25 h. was .75 inch. Several stolons were laid on a flat surface of damp

sand, in the same manner as with those of the strawberry. The friction

of the sand did not interfere with their circumnutation; nor could we

detect any evidence of their being sensitive to contact. In order to

see how in a state of nature they would act, when encountering a stone

or other obstacle on the ground, short pieces of smoked glass, an inch

in height, were stuck upright into the sand in front of two thin

lateral branches. Their tips scratched the smoked surface in various

directions; one made three upward and two downward lines, besides a

nearly horizontal one; the other curled quite away from the glass; but

ultimately both surmounted the glass and pursued their original course.

The apex of a third thick stolon swept up the glass in a curved line,

recoiled and again came into contact with it; it then moved to the

right, and after ascending, descended vertically; ultimately it passed

round one end of the glass instead of over it.

Fig. 88. Saxifraga sarmentosa: circumnutation of an inclined stolon,

traced in darkness on a horizontal glass, from 7.45 A.M. April 18th to

9 A.M. on 19th. Movement of end of stolon magnified 2.2 times.

Many long pins were next driven rather close together into the sand, so

as to form a crowd in front of the same two thin lateral branches; but

these easily wound their way through the crowd. A thick stolon was much

delayed in its passage; at one place it was forced to turn at right

angles to its former course; at another place it could not pass through

the pins, and the hinder part became bowed; it then curved upwards and

passed through an opening between the upper part of some pins which

happened to diverge; it then descended and finally emerged through the

crowd. This stolon was rendered permanently sinuous to a slight degree,

and was thicker where sinuous than elsewhere, apparently from its

longitudinal growth having been checked.

Cotyledon umbilicus (Crassulaceæ).—A plant growing in a pan

of damp moss had emitted 2 stolons, 22 and 20 inches in length. One of

these was supported, so that a length of 4½ inches projected in a

straight and horizontal line, and the movement of the apex was traced.

The first dot was made at 9.10 A.M.; the terminal portion soon began to

bend downwards and continued to do so until noon. Therefore a straight

line, very nearly as long as the whole figure here given (Fig. 89), was

first traced on the glass; but the upper part of this line has not been

copied in the diagram. The curvature occurred in the middle

of the penultimate internode; and its chief seat was at the distance of

1 1/4 inch from the apex; it appeared due to the weight of the terminal

portion, acting on the more flexible part of the internode, and not to

geotropism. The apex after thus sinking down from 9.10 A.M. to noon,

moved a little to the left; it then rose up and circumnutated in a

nearly vertical plane until 10.35 P.M. On the following day (26th) it

was observed from 6.40 A.M. to 5.20 P.M., and within this time it moved

twice up and twice down. On the morning of the 27th the apex stood as

high as it did at 11.30 A.M. on the 25th. Nor did it sink down during

the 28th, but continued to circumnutate about the same place.

Fig. 89. Cotyledon umbilicus: circumnutation of stolon, traced from

11.15 A.M. Aug. 25th to 11 A.M. 27th. Plant illuminated from above. The

terminal internode was .25 inch in length, the penultimate 2.25 and the

third 3.0 inches in length. Apex of stolon stood at a distance of 5.75

inches from the vertical glass; but it was not possible to ascertain

how much the tracing was magnified, as it was not known how great a

length of the internode circumnutated.

Another stolon, which resembled the last in almost every

respect, was observed during the same two days, but only two inches of

the terminal portion was allowed to project freely and horizontally. On

the 25th it continued from 9.10 A.M. to 1.30 P.M. to bend straight

downwards, apparently owing to its weight (Fig. 90); but after this

hour until 10.35 P.M. it zigzagged. This fact deserves notice, for we

here probably see the combined effects of the bending down from weight

and of circumnutation. The stolon, however, did not circumnutate when

it first began to bend down, as may be observed in the present diagram,

and as was still more evident in the last case, when a longer portion

of the stolon was left unsupported. On the following day (26th) the

stolon moved twice up and twice down, but still continued to fall; in

the evening and during the night it travelled from some unknown cause

in an oblique direction.

Fig. 90. Cotyledon umbilicus: circumnutation and downward movement of

another stolon, traced on vertical glass, from 9.11 A.M. Aug. 25th to

11 A.M. 27th. Apex close to glass, so that figure but little magnified,

and here reduced to two-thirds of original size.

We see from these three cases that stolons or runners circumnutate in a

very complex manner. The lines generally extend in a vertical plane,

and this may probably be attributed to the effect of the weight of the

unsupported end of the stolon; but there is always some, and

occasionally a considerable, amount of lateral movement. The

circumnutation is so great in amplitude that it may almost be compared

with that of climbing plants. That the stolons are thus aided in

passing over obstacles and in winding between the stems of the

surrounding plants, the observations above given render almost certain.

If they had not circumnutated, their tips would have been liable to

have been doubled up, as often as they met with obstacles in their

path; but as it is, they easily avoid them. This must be a considerable

advantage to the plant in spreading from its parent-stock; but we are

far from supposing that the power has been gained by the stolons for

this purpose, for circumnutation seems to be of universal occurrence

with all growing parts; but it is not improbable that the amplitude of

the movement may have been specially increased for this purpose.

CIRCUMNUTATION OF FLOWER-STEMS.

We did not think it necessary to make any special observations on the

circumnutation of flower-stems, these being axial in their nature, like

stems or stolons; but some were incidentally made whilst attending to

other subjects, and these we will here briefly give. A few observations

have also been made by other botanists. These taken together suffice to

render it probable that all peduncles and sub-peduncles circumnutate

whilst growing.

Oxalis carnosa.—The peduncle which springs from the thick and woody

stem of this plant bears three or four sub-peduncles. A filament with

little triangles of paper was fixed within the calyx of a flower which

stood upright. Its movements were observed for 48 h.; during the first

half of this time the flower was fully expanded, and during the second

half withered. The figure here given (Fig. 91) represents 8 or 9

ellipses. Although the main peduncle circumnutated, and described one

large and

two smaller ellipses in the course of 24 h., yet the chief seat of

movement lies in the sub-peduncles, which ultimately bend vertically

downwards, as will be described in a future chapter. The peduncles of

Oxalis acetosella likewise bend downwards, and afterwards, when the

pods are nearly mature, upwards; and this is effected by a

circumnutating movement.

Fig. 91. Oxalis carnosa: flower-stem, feebly illuminated from above,

its circumnutation traced from 9 A.M. April 13th to 9 A.M. 15th. Summit

of flower 8 inches beneath the horizontal glass. Movement probably

magnified about 6 times.

It may be seen in the above figure that the flower-stem of O. carnosa

circumnutated during two days about the same spot. On the other hand,

the flower-stem of O. sensitiva undergoes a strongly marked, daily,

periodical change of position, when kept at a proper temperature. In

the middle of the day it stands vertically up, or at a high angle; in

the afternoon it sinks, and in the evening projects horizontally, or

almost horizontally, rising again during the night. This movement

continues from the period when the flowers are in bud to when, as we

believe, the pods are mature: and it ought perhaps to have been

included amongst the so-called sleep-movements of plants. A tracing was

not made, but the angles were measured at successive periods during one

whole day; and these showed that the movement was not continuous, but

that the peduncle oscillated up and down. We may therefore conclude

that it circumnutated. At the base of the peduncle there is a mass of

small cells, forming a well-developed pulvinus, which is exteriorly

coloured purple and hairy. In no other genus, as far as we know, is the

peduncle furnished with a pulvinus. The peduncle of O. Ortegesii

behaved differently from that of O. sensitiva, for it stood at a less

angle above the horizon in the middle of the day, then in the morning

or evening. By 10.20 P.M. it had risen greatly. During the middle of

the day it oscillated much up and down.

Trifolium subterraneum.—A filament was fixed vertically to the

uppermost part of the peduncle of a young and upright flower-head (the

stem of the plant having been secured to a stick); and its movements

were traced during 36 h. Within this time it described (see Fig. 92) a

figure which represents four ellipses; but during the latter part of

the time the peduncle began to bend downwards, and after 10.30 P.M. on

the 24th it curved so rapidly down, that by 6.45 A.M. on the 25th it

stood only 19° above the horizon. It went on circumnutating in nearly

the same position for two days. Even after the flower-heads have buried

themselves in the ground they continue, as will hereafter be shown, to

circumnutate. It will also be seen in the next chapter that the

sub-peduncles of the separate flowers of

_Trifolium repens_ circumnutate in a complicated course during several

days. I may add that the gynophore of _Arachis hypogoea_, which looks

exactly like a peduncle, circumnutates whilst growing vertically

downwards, in order to bury the young pod in the ground.

Fig. 92. Trifolium subterraneum: main flower-peduncle, illuminated from

above, circumnutation traced on horizontal glass, from 8.40 A.M. July

23rd to 10.30 P.M. 24th.

The movements of the flowers of Cyclamen Persicum were not observed;

but the peduncle, whilst the pod is forming, increases much in length,

and bows itself down by a circumnutating movement. A young peduncle of

Maurandia semperflorens, 1½ inch in length, was carefully observed

during a whole day, and it made 4½ narrow, vertical, irregular and

short ellipses, each at an average rate of about 2 h. 25 m. An

adjoining peduncle described during the same time similar, though

fewer, ellipses.[4] According to Sachs[5] the flower-stems, whilst

growing,

of many plants, for instance, those of Brassica napus, revolve or

circumnutate; those of Allium porrum bend from side to side, and, if

this movement had been traced on a horizontal glass, no doubt ellipses

would have been formed. Fritz Müller has described[6] the spontaneous

revolving movements of the flower-stems of an Alisma, which he compares

with those of a climbing plant.

[4] ‘The Movements and Habits of Climbing Plants,’ 2nd edit., 1875, p.

68.

[5] ‘Text-Book of Botany,’ 1875, p. 766. Linnæus and Treviranus

(according to Pfeffer, ‘Die Periodischen Bewegungen,’ etc., p. 162)

state that the flower-stalks of many plants occupy different positions

by night and day, and we shall see in the chapter on the Sleep of

Plants that this implies circumnutation.

[6] ‘Jenaische Zeitsch.,’ B. v. p. 133.

We made no observations on the movements of the different parts of

flowers. Morren, however, has observed[7] in the stamens of Sparmannia

and Cereus a “fremissement spontané,” which, it may be suspected, is a

circumnutating movement. The circumnutation of the gynostemium of

Stylidium, as described by Gad,[8] is highly remarkable, and apparently

aids in the fertilisation of the flowers. The gynostemium, whilst

spontaneously moving, comes into contact with the viscid labellum, to

which it adheres, until freed by the increasing tension of the parts or

by being touched.

[7] ‘N. Mem. de l’Acad. R. de Bruxelles,’ tom. xiv. 1841, p. 3.

[8] ‘Sitzungbericht des bot. Vereins der P. Brandenburg,’ xxi. p. 84.

We have now seen that the flower-stems of plants belonging to such

widely different families as the Cruciferae, Oxalidæ, Leguminosae,

Primulaceae, Scrophularineae, Alismaceae, and Liliaceae, circumnutate;

and that there are indications of this movement in many other families.

With these facts before us, bearing also in mind that the tendrils of

not a few plants consist of modified peduncles, we may admit without

much doubt that all growing flower-stems circumnutate.

CIRCUMNUTATION OF LEAVES: DICOTYLEDONS.

Several distinguished botanists, Hofmeister, Sachs, Pfeffer, De Vries,

Batalin, Millardet, etc., have

observed, and some of them with the greatest care, the periodical

movements of leaves; but their attention has been chiefly, though not

exclusively, directed to those which move largely and are commonly said

to sleep at night. From considerations hereafter to be given, plants of

this nature are here excluded, and will be treated of separately. As we

wished to ascertain whether all young and growing leaves circumnutated,

we thought that it would be sufficient if we observed between 30 and 40

genera, widely distributed throughout the vegetable series, selecting

some unusual forms and others on woody plants. All the plants were

healthy and grew in pots. They were illuminated from above, but the

light perhaps was not always sufficiently bright, as many of them were

observed under a skylight of ground-glass. Except in a few specified

cases, a fine glass filament with two minute triangles of paper was

fixed to the leaves, and their movements were traced on a vertical

glass (when not stated to the contrary) in the manner already

described. I may repeat that the broken lines represent the nocturnal

course. The stem was always secured to a stick, close to the base of

the leaf under observation. The arrangement of the species, with the

number of the Family appended, is the same as in the case of stems.

Fig. 93. Sarracenia purpurea: circumnutation of young pitcher, traced

from 8 A.M. July 3rd to 10.15 A.M. 4th. Temp. 17°–18° C. Apex of

pitcher 20 inches from glass, so movement greatly magnified.

(1.) Sarracenia purpurea (Sarraceneae, Fam. 11).—A young leaf, or

pitcher, 8½ inches in height, with the bladder swollen but with the

hood not as yet open, had a filament fixed transversely

across its apex; it was observed for 48 h., and during the whole of

this time it circumnutated in a nearly similar manner, but to a very

small extent. The tracing given (Fig. 93) relates only to the movement

during the first 26 h.

(2) Glaucium luteum (Papaveraceae, Fam. 12).—A young plant, bearing

only 8 leaves, had a filament attached to the youngest leaf but one,

which was 3 inches in length, including the petiole. The circumnutating

movement was traced during 47 h. On both days the leaf descended from

before 7 A.M. until about 11 A.M., and then ascended slightly during

the rest of the day and the early part of the night. During the latter

part of the night it fell greatly. It did not ascend so much during the

second as during the first day, and it descended considerably lower on

the second night than on the first. This difference was probably due to

the illumination from above having been insufficient during the two

days of observation. Its course during the two days is shown in Fig.

94.

Fig. 94. Glaucium luteum: circumnutation of young leaf, traced from

9.30 A.M. June 14th to 8.30 A.M. 16th. Tracing not much magnified, as

apex of leaf stood only 5½ inches from the glass.

(3.) Crambe maritima (Cruciferae, Fam. 14).—A leaf 9½ inches in length

on a plant not growing vigorously was first observed. Its apex was in

constant movement, but this could hardly be traced, from being so small

in extent. The apex, however, certainly changed its course at least 6

times in the course of 14 h. A more vigorous young plant, bearing only

4 leaves, was then selected, and a filament was affixed to the midrib

of the third leaf from the base, which, with the petiole, was 5 inches

in length. The leaf stood up almost vertically, but the tip

was deflected, so that the filament projected almost horizontally, and

its movements were traced during 48 h. on a vertical glass as shown in

the accompanying figure (Fig. 95). We here plainly see that the leaf

was continually circumnutating; but the proper periodicity of its

movements was disturbed by its being only dimly illuminated from above

through a double skylight. We infer that this was the case, because two

leaves on plants growing out of doors, had their angles above the

horizon measured in the middle of the day and at 9 to about 10 P.M. on

successive nights, and they were found at this latter hour to have

risen by an average angle of 9° above their mid-day position: on the

following morning they fell to their former position. Now it may be

observed in the diagram that the leaf rose during the second night, so

that it stood at 6.40 A.M. higher than at 10.20 P.M. on the preceding

night; and this may be attributed to the leaf adjusting itself to the

dim light, coming exclusively from above.

Fig. 95. Crambe maritima: circumnutation of leaf, disturbed by being

insufficiently illuminated from above, traced from 7.50 A.M. June 23rd

to 8 A.M. 25th. Apex of leaf 15 1/4 inches from the vertical glass, so

that the tracing was much magnified, but is here reduced to one-fourth

of original scale.

(4.) Brassica oleracea (Cruciferae).—Hofmeister and Batalin[9] state

that the leaves of the cabbage rise at night, and fall by day. We

covered a young plant, bearing 8 leaves, under a large bell-glass,

placing it in the same position with respect to the

light in which it had long remained, and a filament was fixed at the

distance of .4 of an inch from the apex of a young leaf nearly 4 inches

in length. Its movements were then traced during three days, but the

tracing is not worth giving. The leaf fell during the whole morning,

and rose in the evening and during the early part of the night. The

ascending and descending lines did not coincide, so that an irregular

ellipse was formed each 24 h. The basal part of the midrib did not

move, as was ascertained by measuring at successive periods the angle

which it formed with the horizon, so that the movement was confined to

the terminal portion of the leaf, which moved through an angle of 11°

in the course of 24 h., and the distance travelled by the apex, up and

down, was between .8 and .9 of an inch.

[9] ‘Flora,’ 1873, p. 437.

In order to ascertain the effect of darkness, a filament was fixed to a

leaf 5½ inches in length, borne by a plant which after forming a head

had produced a stem. The leaf was inclined 44° above the horizon, and

its movements were traced on a vertical glass every hour by the aid of

a taper. During the first day the leaf rose from 8 A.M. to 10.40 P.M.

in a slightly zigzag course, the actual distance travelled by the apex

being .67 of an inch. During the night the leaf fell, whereas it ought

to have risen; and by 7 A.M. on the following morning it had fallen .23

of an inch, and it continued falling until 9.40 A.M. It then rose until

10.50 P.M., but the rise was interrupted by one considerable

oscillation, that is, by a fall and re-ascent. During the second night

it again fell, but only to a very short distance, and on the following

morning re-ascended to a very short distance. Thus the normal course of

the leaf was greatly disturbed, or rather completely inverted, by the

absence of light; and the movements were likewise greatly diminished in

amplitude.

We may add that, according to Mr. A. Stephen Wilson,[10] the young

leaves of the Swedish turnip, which is a hybrid between B. oleracea and

rapa, draw together in the evening so much “that the horizontal breadth

diminishes about 30 per cent. of the daylight breadth.” Therefore the

leaves must rise considerably at night.

[10] ‘Trans. Bot. Soc. Edinburgh,’ vol. xiii. p. 32. With respect to

the origin of the Swedish turnip, see Darwin, ‘Animals and Plants

under Domestication,’ 2nd edit. vol. i. p. 344.

(5.) Dianthus caryophyllus (Caryophylleae, Fam. 26).—The

terminal shoot of a young plant, growing very vigorously, was selected

for observation. The young leaves at first stand up vertically and

close together, but they soon bend outwards and downwards, so as to

become horizontal, and often at the same time a little to one side. A

filament was fixed to the tip of a young leaf whilst still highly

inclined, and the first dot was made on the vertical glass at 8.30 A.M.

June 13th, but it curved downwards so quickly that by 6.40 A.M. on the

following morning it stood only a little above the horizon. In Fig. 96

the long, slightly zigzag line representing this rapid downward course,

which was somewhat inclined to the left, is not given; but the figure

shows the highly tortuous and zigzag course, together with some loops,

pursued during the next 2½ days. As the leaf continued to move all the

time to the left, it is evident that the zigzag line represents many

circumnutations.

Fig. 96. Dianthus caryophyllus: circumnutation of young leaf, traced

from 10.15 P.M. June 13th to 10.35 P.M. 16th. Apex of leaf stood, at

the close of our observations, 8 3/4 inches from the vertical glass, so

tracing not greatly magnified. The leaf was 5 1/4 inches long. Temp.

15½°–17½° C.

(6.) Camellia Japonica (Camelliaceae, Fam. 32).—A youngish leaf, which

together with its petiole was 2 3/4 inches in length and which arose

from a side branch on a tall bush, had a filament attached to its apex.

This leaf sloped downwards at an angle of 40° beneath the horizon. As

it was thick and rigid, and its

petiole very short, much movement could not be expected. Nevertheless,

the apex changed its course completely seven times in the course of 11½

h., but moved to only a very small distance. On the next day the

movement of the apex was traced during 26 h. 20 m. (as shown in Fig.

97), and was nearly of the same nature, but rather less complex. The

movement seems to be periodical, for on both days the leaf

circumnutated in the forenoon, fell in the afternoon (on the first day

until between 3 and 4 P.M., and on the second day until 6 P.M.), and

then rose, falling again during the night or early morning.

Fig. 97. Camellia Japonica: circumnutation of leaf, traced from 6.40

A.M. June 14th to 6.50 A.M. 15th. Apex of leaf 12 inches from the

vertical glass, so figure considerably magnified. Temp. 16°–16½° C.

In the chapter on the Sleep of Plants we shall see that the leaves in

several Malvaceous genera sink

Fig. 98. Pelargonium zonale: circumnutation and downward movement of

young leaf, traced from 9.30 A.M. June 14th to 6.30 P.M. 16th. Apex of

leaf 9 1.4 inches from the vertical glass, so figure moderately

magnified. Temp. 15°–16½° C.

at night; and as they often do not then occupy a vertical position,

especially if they have not been well illuminated during

the day, it is doubtful whether some of these cases ought not to have

been included in the present chapter.

(7.) Pelargonium zonale (Geraniaceae, Fam. 47).—A young leaf, 1 1/4

inch in breadth, with its petiole 1 inch long, borne on a young plant,

was observed in the usual manner during 61 h.; and its course is shown

in the preceding figure (Fig. 98). During the first day and night the

leaf moved downwards, but circumnutated between 10 A.M. and 4.30 P.M.

On the second day it sank and rose again, but between 10 A.M. and 6

P.M. it circumnutated on an extremely small scale. On the third day the

circumnutation was more plainly marked.

(8.) Cissus discolor (Ampelideae, Fam. 67).—A leaf, not nearly

full-grown, the third from the apex of a shoot on a cut-down plant, was

observed during 31 h. 30 m. (see Fig. 99). The day was cold (15°–16°

C.), and if the plant had been observed in the hot-house, the

circumnutation, though plain enough as it was, would probably have been

far more conspicuous.

Fig. 99. Cissus discolor: circumnutation of leaf, traced from 10.35

A.M. May 28th to 6 P.M. 29th. Apex of leaf 8 3/4 inches from the

vertical glass.

(9.) Vicia faba (Leguminosae, Fam. 75).—A young leaf, 3.1 inches in

length, measured from base of petiole to end of leaflets, had a

filament affixed to the midrib of one of the two terminal leaflets, and

its movements were traced during 51½ h. The filament fell all morning

(July 2nd) till 3 P.M., and then rose greatly till 10.35 P.M.; but the

rise this day was so great, compared with that which subsequently

occurred, that it was probably due in part to the plant being

illuminated from above. The latter part of the course on July 2nd is

alone given in the following figure (Fig. 100). On the next day (July

3rd) the leaf again fell in the morning, then circumnutated in a

conspicuous manner, and rose till late at night; but the movement was

not traced after 7.15 P.M., as by that time the filament pointed

towards the upper edge of the glass. During the latter part of the

night or early morning it again fell in the same manner as before.

As the evening rise and the early morning fall were unusually large,

the angle of the petiole above the horizon was measured at the two

periods, and the leaf was found to have risen 19° between 12.20 P.M.

and 10.45 P.M., and to have fallen 23° 30 seconds between the latter

hour and 10.20 A.M. on the following morning.

Fig. 100. Vicia faba: circumnutation of leaf, traced from 7.15 P.M.

July 2nd to 10.15 A.M. 4th. Apex of the two terminal leaflets 7 1/4

inches from the vertical glass. Figure here reduced to two-thirds of

original scale. Temp. 17°–18° C.

The main petiole was now secured to a stick close to the base

of the two terminal leaflets, which were 1.4 inch in length; and the

movements of one of them were traced during 48 h. (see Fig. 101). The

course pursued is closely analogous to that of the whole leaf. The

zigzag line between 8.30 A.M. and 3.30 P.M. on the second day

represents 5 very small ellipses, with their longer axes differently

directed. From these observations it follows that both the whole leaf

and the terminal leaflets undergo a well-marked daily periodical

movement, rising in the evening and falling during the latter part of

the night or early morning; whilst in the middle of the day they

generally circumnutate round the same small space.

Fig 101. Vicia faba: circumnutation of one of the two terminal

leaflets, the main petiole having been secured, traced from 10.40 A.M.

July 4th to 10.30 A.M. 6th. Apex of leaflet 6 5/8 inches from the

vertical glass. Tracing here reduced to one-half of original scale.

Temp. 16°–18° C.

(10.) Acacia retinoides (Leguminosae).—The movement of a young

phyllode, 2 3/8 inches in length, and inclined at a considerable angle

above the horizon, was traced during 45 h. 30 m.; but in the figure

here given (Fig. 102), its circumnutation is shown during only 21 h. 30

m. During part of this time (viz., 14 h. 30 m.) the phyllode described

a figure representing 5 or 6 small ellipses. The actual amount of

movement in a vertical direction was .3 inch. The phyllode rose

considerably between 1.30 P.M. and 4 P.M., but there was no evidence on

either day of a regular periodic movement.

Fig. 102. Acacia retinoides: circumnutation of a young phyllode, traced

from 10.45 A.M. July 18th to 8.15 A.M. 19th. Apex of phyllode 9 inches

from the vertical glass; temp. 16½°–17½° C.

(11.) Lupinus speciosus (Leguminosae).—Plants were raised from seed

purchased under this name. This is one of the species in this large

genus, the leaves of which do not sleep at night. The petioles rise

direct from the ground, and are from 5 to 7 inches in length. A

filament was fixed to the midrib of one of the longer leaflets, and the

movement of the whole leaf was traced, as shown in Fig. 103. In the

course of 6 h. 30 m. the filament went four times up and three times

down. A new tracing was then begun (not here given), and during 12½ h.

the leaf moved eight times up and seven times down; so that it

described 7½ ellipses in this time, and this is an extraordinary rate

of movement. The summit of the petiole was then secured to a stick, and

the separate leaflets were found to be continually circumnutating.

Fig. 103. Lupinus speciosus: circumnutation of leaf, traced on vertical

glass, from 10.15 A.M. to 5.45 P.M.; i.e., during 6 h. 30 m.

(12.) Echeveria stolonifera (Crassulaceæ, Fam. 84).—The older leaves of

this plant are so thick and fleshy, and the young ones so short and

broad, that it seemed very improbable that any circumnutation could be

detected. A filament was fixed to a young upwardly inclined leaf, .75

inch in length and .28 in breadth, which stood on the outside of a

terminal rosette of leaves, produced by a plant growing very

vigorously. Its movement was traced during 3 days, as here shown (Fig.

104). The course was chiefly in an upward direction, and this may be

attributed to the elongation of the leaf through growth; but we see

that the lines are strongly zigzag, and that occasionally there was

distinct circumnutation, though on a very small scale.

Fig. 104. Echeveria stolonifera: circumnutation of leaf, traced from

8.20 A.M. June 25th to 8.45 A.M. 28th. Apex of leaf 12 1/4 inches from

the glass, so that the movement was much magnified; temp. 23°–24½° C.

(13.) Bryophyllum (vel Calanchæ) calycinum (Crassulaceæ).—Duval-Jouve

(‘Bull. Soc. Bot. de France,’ Feb. 14th, 1868) measured the distance

between the tips of the upper pair of leaves on this plant, with the

result shown in the following Table. It should be noted that the

measurements on Dec. 2nd were made on a different pair of leaves:—

8 A.M. 2 P.M. 7 P.M. Nov. 16. . . . . . . . . . . . . . . . .

. .15 mm.. . . . . .25 mm. . . .. . . .(?) ” 19. . . . . . . . . .

. . . . . . . . .48 ” . . . . . . . 60 ”. . . . . . . 48 mm. Dec.

2. . . . . . . . . . . . . . . . . . .22 ”. . . . . . . . 43 ”. . . .

. . . .28 ”

We see from this Table that the leaves stood considerably further apart

at 2 P.M. than at either 8 A.M. or 7 P.M.; and this shows that they

rise a little in the evening and fall or open in the forenoon.

(14.) Drosera rotundifolia (Droseraceae, Fam. 85).—The movements of a

young leaf, having a long petiole but with its tentacles (or

gland-bearing hairs) as yet unfolded, were traced during 47 h. 15 m.

The figure (Fig. 105) shows that it circumnutated largely, chiefly in a

vertical direction, making two ellipses each

day. On both days the leaf began to descend after 12 or 1 o’clock, and

continued to do so all night, though to a very unequal distance on the

two occasions. We therefore thought that the movement was periodic; but

on observing three other leaves during several successive days and

nights, we found this to be an error; and the case is given merely as a

caution. On the third morning the above leaf occupied almost exactly

the same position as on the first morning; and the tentacles by this

time had unfolded sufficiently to project at right angles to the blade

or disc.

Fig. 105. Drosera rotundifolia: circumnutation of young leaf, with

filament fixed to back of blade, traced from 9.15 A.M. June 7th to 8.30

A.M. June 9th. Figure here reduced to one-half original scale.

The leaves as they grow older generally sink more and more downwards.

The movement of an oldish leaf, the glands of which were still

secreting freely, was traced for 24 h., during which time it continued

to sink a little in a slightly zigzag line. On the following morning,

at 7 A.M., a drop of a solution of carbonate of ammonia (2 gr. to 1 oz.

of water) was placed on the disc, and this blackened the glands and

induced inflection of many of the tentacles. The weight of the drop

caused the leaf at first to sink a little; but immediately afterwards

it began to rise in a somewhat zigzag course, and continued to do so

till 3 P.M. It then circumnutated about the same spot on a very small

scale for 21 h.; and during the next 21 h. it sank in a zigzag line to

nearly the same level which it had held when the ammonia was first

administered. By this time the tentacles had re-expanded, and the

glands had recovered their proper colour. We thus learn that an old

leaf

circumnutates on a small scale, at least whilst absorbing carbonate of

ammonia; for it is probable that this absorption may stimulate growth

and thus re-excite circumnutation. Whether the rising of the glass

filament which was attached to the back of the leaf, resulted from its

margin becoming slightly inflected (as generally occurs), or from the

rising of the petiole, was not ascertained.

In order to learn whether the tentacles or gland-bearing hairs

circumnutate, the back of a young leaf, with the innermost tentacles as

yet incurved, was firmly cemented with shellac to a flat stick driven

into compact damp argillaceous sand. The plant was placed under a

microscope with the stage removed and with an eye-piece micrometer, of

which each division equalled 1/500 of an inch. It should be stated that

as the leaves grow older the tentacles of the exterior rows bend

outwards and downwards, so as ultimately to become deflected

considerably beneath the horizon. A tentacle in the second row from the

margin was selected for observation, and was found to be moving

outwards at a rate of 1/500 of an inch in 20 m., or 1/100 of inch in 1

h. 40 m.; but as it likewise moved from side to side to an extent of

above 1/500 of inch, the movement was probably one of modified

circumnutation. A tentacle on an old leaf was next observed in the same

manner. In 15 m. after being placed under the microscope it had moved

about 1/1000 of an inch. During the next 7½ h. it was looked at

repeatedly, and during this whole time it moved only another 1/1000 of

an inch; and this small movement may have been due to the settling of

the damp sand (on which the plant rested), though the sand had been

firmly pressed down. We may therefore conclude that the tentacles when

old do not circumnutate; yet this tentacle was so sensitive, that in 23

seconds after its gland had been merely touched with a bit of raw meat,

it began to curl inwards. This fact is of some importance, as it

apparently shows that the inflection of the tentacles from the stimulus

of absorbed animal matter (and no doubt from that of contact with any

object) is not due to modified circumnutation.

(15.) Dionoea muscipula (Droseraceae).—It should be premised that the

leaves at an early stage of their development have the two lobes

pressed closely together. These are at first directed back towards the

centre of the plant; but they gradually rise up and soon stand at right

angles to the petiole, and ultimately in nearly a straight line with

it. A young leaf, which with the

petiole was only 1.2 inch in length, had a filament fixed externally

along the midrib of the still closed lobes, which projected at right

angles to the petiole. In the evening this leaf completed an ellipse in

the course of 2 h. On the following day (Sept. 25th) its movements were

traced during 22 h.; and we see in Fig. 106 that it moved in the same

general direction, due to the straightening of the leaf, but in an

extremely zigzag line. This line represents several drawn-out or

modified ellipses. There can therefore be no doubt that this young leaf

circumnutated.

Fig. 106. Dionaea muscipula: circumnutation of a young and expanding

leaf, traced on a horizontal glass in darkness, from noon Sept. 24th to

10 A.M. 25th. Apex of leaf 13½ inches from the glass, so tracing

considerably magnified.

A rather old, horizontally extended leaf, with a filament attached

along the under side of the midrib, was next observed during 7 h. It

hardly moved, but when one of its sensitive hairs was touched, the

blades closed, though not very quickly. A new dot was now made on the

glass, but in the course of 14 h. 20 m. there was hardly any change in

the position of the filament. We may therefore infer that an old and

only moderately sensitive leaf does not circumnutate plainly; but we

shall soon see that it by no means follows that such a leaf is

absolutely motionless. We may further infer that the stimulus from a

touch does not re-excite plain circumnutation.

Another full-grown leaf had a filament attached externally along one

side of the midrib and parallel to it, so that the filament would move

if the lobes closed. It should be first stated that, although a touch

on one of the sensitive hairs of a vigorous leaf causes it to close

quickly, often almost instantly, yet when a bit of damp meat or some

solution of carbonate of ammonia is placed on the lobes, they close so

slowly that generally 24 h. is required for the completion of the act.

The above leaf was first observed for 2 h. 30 m., and did not

circumnutate, but it ought to have been observed for a

longer period; although, as we have seen, a young leaf completed a

fairly large ellipse in 2 h. A drop of an infusion of raw meat was then

placed on the leaf, and within 2 h. the glass filament rose a little;

and this implies that the lobes had begun to close, and perhaps the

petiole to rise. It continued to rise with extreme slowness for the

next 8 h. 30 m. The position of the pot was then (7.15 P.M., Sept.

24th) slightly changed and an additional drop of the infusion given,

and a new tracing was begun (Fig. 107). By 10.50 P.M. the filament had

risen only a little more, and it fell during the night. On the

following morning the lobes were closing more quickly, and by 5 P.M. it

was evident to the eye that they had closed considerably; by 8.48. P.M.

this was still plainer, and by 10.45 P.M. the marginal spikes were

interlocked. The leaf fell a little during the night, and next morning

(25th) at 7 A.M. the lobes were completely shut. The course pursued, as

may be seen in the figure, was strongly zigzag, and this indicates that

the closing of the lobes was combined with the circumnutation of the

whole leaf; and there cannot be much doubt, considering how motionless

the leaf was during 2 h. 30 m. before it received the infusion, that

the absorption of the animal matter had excited it to circumnutate. The

leaf was occasionally observed for the next four days, but was kept in

rather too cool a place; nevertheless, it continued to circumnutate to

a small extent, and the lobes remained closed.

Fig. 107. Dionoea muscipula: closure of the lobes and circumnutation of

a full-grown leaf, whilst absorbing an infusion of raw meat, traced in

darkness, from 7.15 P.M. Sept. 24th to 9 A.M. 26th. Apex of leaf 8½

inches from the vertical glass. Figure here reduced to two-thirds of

original scale.

It is sometimes stated in botanical works that the lobes close or sleep

at night; but this is an error. To test the statement, very long glass

filaments were fixed inside the two lobes of three leaves, and the

distances between their tips were measured in the middle of the day and

at night; but no difference could be detected.

The previous observations relate to the movements of the whole leaf,

but the lobes move independently of the petiole, and

seem to be continually opening and shutting to a very small extent. A

nearly full-grown leaf (afterwards proved to be highly sensitive to

contact) stood almost horizontally, so that by driving a long thin pin

through the foliaceous petiole close to the blade, it was rendered

motionless. The plant, with a little triangle of paper attached to one

of the marginal spikes, was placed under a microscope with an eye-piece

micrometer, each division of which equalled 1/500 of an inch. The apex

of the paper-triangle was now seen to be in constant slight movement;

for in 4 h. it crossed nine divisions, or 9/500 of an inch, and after

ten additional hours it moved back and had crossed 5/500 in an opposite

direction. The plant was kept in rather too cool a place, and on the

following day it moved rather less, namely, 1/500 in 3 h., and 2/500 in

an opposite direction during the next 6 h. The two lobes, therefore,

seem to be constantly closing or opening, though to a very small

distance; for we must remember that the little triangle of paper

affixed to the marginal spike increased its length, and thus

exaggerated somewhat the movement. Similar observations, with the

important difference that the petiole was left free and the plant kept

under a high temperature, were made on a leaf, which was healthy, but

so old that it did not close when its sensitive hairs were repeatedly

touched, though judging from other cases it would have slowly closed if

it had been stimulated by animal matter. The apex of the triangle was

in almost, though not quite, constant movement, sometimes in one

direction and sometimes in an opposite one; and it thrice crossed five

divisions of the micrometer (i.e. 1/100 of an inch) in 30 m. This

movement on so small a scale is hardly comparable with ordinary

circumnutation; but it may perhaps be compared with the zigzag lines

and little loops, by which the larger ellipses made by other plants are

often interrupted.

In the first chapter of this volume, the remarkable oscillatory

movements of the circumnutating hypocotyl of the cabbage have been

described. The leaves of Dionaea present the same phenomenon, which is

a wonderful one, as viewed under a low power (2-inch object-glass),

with an eye-piece micrometer of which each division (1/500 of an inch)

appeared as a rather wide space. The young unexpanded leaf, of which

the circumnutating movements were traced (Fig. 106), had a glass

filament fixed perpendicularly to it; and the movement of the apex was

observed in the hot-house (temp. 84° to 86° F.), with light admitted

only from above, and with any lateral currents of air

excluded. The apex sometimes crossed one or two divisions of the

micrometer at an imperceptibly slow rate, but generally it moved

onwards by rapid starts or jerks of 2/1000 or 3/1000, and in one

instance of 4/1000 of an inch. After each jerk forwards, the apex drew

itself backwards with comparative slowness for part of the distance

which had just been gained; and then after a very short time made

another jerk forwards. Four conspicuous jerks forwards, with slower

retreats, were seen on one occasion to occur in exactly one minute,

besides some minor oscillations. As far as we could judge, the

advancing and retreating lines did not coincide, and if so, extremely

minute ellipses were each time described. Sometimes the apex remained

quite motionless for a short period. Its general course during the

several hours of observation was in two opposite directions, so that

the leaf was probably circumnutating.

An older leaf with the lobes fully expanded, and which was afterwards

proved to be highly sensitive to contact, was next observed in a

similar manner, except that the plant was exposed to a lower

temperature in a room. The apex oscillated forwards and backwards in

the same manner as before; but the jerks forward were less in extent,

viz. about 1/1000 inch; and there were longer motionless periods. As it

appeared possible that the movements might be due to currents of air, a

wax taper was held close to the leaf during one of the motionless

periods, but no oscillations were thus caused. After 10 m., however,

vigorous oscillations commenced, perhaps owing to the plant having been

warmed and thus stimulated. The candle was then removed and before long

the oscillations ceased; nevertheless, when looked at again after an

interval of 1 h. 30 m., it was again oscillating. The plant was taken

back into the hot-house, and on the following morning was seen to be

oscillating, though not very vigorously. Another old but healthy leaf,

which was not in the least sensitive to a touch, was likewise observed

during two days in the hot-house, and the attached filament made many

little jerks forwards of about 2/1000 or only 1/1000 of an inch.

Finally, to ascertain whether the lobes independently of the petiole

oscillated, the petiole of an old leaf was cemented close to the blade

with shellac to the top of a little stick driven into the soil. But

before this was done the leaf was observed, and found to be vigorously

oscillating or jerking; and after it had been cemented to the stick,

the oscillations of about 2/1000 of an inch still continued. On the

following day a little infusion

of raw meat was placed on the leaf, which caused the lobes to close

together very slowly in the course of two days; and the oscillations

continued during this whole time and for the next two days. After nine

additional days the leaf began to open and the margins were a little

everted, and now the apex of the glass filament remained for long

periods motionless, and then moved backwards and forwards for a

distance of about 1/1000 of an inch slowly, without any jerks.

Nevertheless, after warming the leaf with a taper held close to it, the

jerking movement recommenced.

This same leaf had been observed 2½ months previously, and was then

found to be oscillating or jerking. We may therefore infer that this

kind of movement goes on night and day for a very long period; and it

is common to young unexpanded leaves and to leaves so old as to have

lost their sensitiveness to a touch, but which were still capable of

absorbing nitrogenous matter. The phenomenon when well displayed, as in

the young leaf just described, is a very interesting one. It often

brought before our minds the idea of effort, or of a small animal

struggling to escape from some constraint.

(16.) Eucalyptus resinifera (Myrtaceae, Fam. 94).—A young leaf, two

inches in length together with the petiole, produced by a lateral shoot

from a cut-down tree, was observed in the usual manner. The blade had

not as yet assumed its vertical position. On June 7th only a few

observations were made, and the tracing merely showed that the leaf had

moved three times upwards and three downwards. On the following day it

was observed more frequently; and two tracings were made (see A and B,

Fig. 108), as a single one would have been too complicated. The apex

changed its course 13 times in the course of 16 h., chiefly up and

down, but with some lateral movement. The actual amount of movement in

any one direction was small.

Fig. 108. Eucalyptus resinifera: circumnutation of a leaf, traced, A,

from 6.40 A.M. to 1 P.M. June 8th; B, from 1 P.M. 8th to 8.30 A.M. 9th.

Apex of leaf 14½ inches from the horizontal glass, so figures

considerably magnified.

(17.) Dahlia (garden var.) (Compositæ, Fam. 122).—A fine young

leaf 5 3/4 inches in length, produced by a young plant 2 feet high,

growing vigorously in a large pot, was directed at an angle of about

45° beneath the horizon. On June 18th the leaf descended from 10 A.M.

till 11.35 A.M. (see Fig. 109); it then ascended greatly till 6 P.M.,

this ascent being probably due to the light coming only from above. It

zigzagged between 6 P.M. and 10.35 P.M., and ascended a little during

the night. It should be remarked that the vertical distances in the

lower part of the diagram are much exaggerated, as the leaf was at

first deflected beneath the horizon, and after it had sunk downwards,

the filament pointed in a very oblique line towards the glass. Next

day the leaf descended from 8.20 A.M. till 7.15 P.M., then zigzagged

and ascended greatly during the night. On the morning of the 20th the

leaf was probably beginning to descend, though the short line in the

diagram is horizontal. The actual distances travelled by the apex of

the leaf were considerable, but could not be calculated with safety.

From the course pursued on the second day, when the plant had

accommodated itself to the light from above, there cannot be much doubt

that the leaves undergo a daily periodic movement, sinking during the

day and rising at night.

Fig. 109. Dahlia: circumnutation of leaf, traced from 10 A.M. June 18th

to 8.10 A.M. 20th, but with a break of 1 h. 40 m. on the morning of the

19th, as, owing to the glass filament pointing too much to one side,

the pot had to be slightly moved; therefore the relative position of

the two tracings is somewhat arbitrary. The figure here given is

reduced to one-fifth of the original scale. Apex of leaf 9 inches from

the glass in the line of its inclination, and 4 3/4 in a horizontal

line.

(18.) Mutisia clematis (Compositæ).—The leaves terminate in tendrils

and circumnutate like those of other tendril-bearers; but this plant is

here mentioned, on account of an erroneous statement[11] which has been

published, namely, that the leaves sink at night and rise during the

day. The leaves which behaved in this manner had been kept for some

days in a northern room and had not been sufficiently illuminated. A

plant therefore was left undisturbed in the hot-house, and three leaves

had their angles measured at noon and at 10 P.M. All three were

inclined a little beneath the horizon at noon, but one stood at night

2°, the second 21°, and the third 10° higher than in the middle of the

day; so that instead of sinking they rise a little at night.

[11] ‘The Movements and Habits of Climbing Plants,’ 1875, p. 118.

(19.) Cyclamen Persicum (Primulaceae, Fam. 135).—A young leaf, 1.8 of

an inch in length, petiole included, produced by an old root-stock, was

observed during three days in the usual manner (Fig. 110). On the first

day the leaf fell more than afterwards, apparently from adjusting

itself to the light from above. On all three days it fell from the

early morning to about 7 P.M., and from that hour rose during the

night, the course being slightly zigzag. The movement therefore is

strictly periodic. It should be noted that the leaf would have sunk

each evening a little lower down than it did, had not the glass

filament rested between 5 and 6 P.M. on the rim of the pot. The amount

of movement was considerable; for if we assume that the whole leaf to

the base of the petiole became bent, the tracing would be magnified

rather less than five times, and this would give to the apex a rise and

fall of half an inch, with some lateral movement. This amount, however,

would not attract attention without the aid of a tracing or measurement

of some kind.

(20.) Allamanda Schottii (Apocyneae, Fam. 144).—The young leaves of

this shrub are elongated, with the blade bowed so much downwards as

almost to form a semicircle. The chord—that is, a line drawn from the

apex of the blade to the base of the petiole—of a young leaf, 4 3/4

inches in length, stood at 2.50 P.M. on

Dec. 5th at an angle of 13° beneath the horizon, but by 9.30 P.M. the

blade had straightened itself so much, which implies the raising of the

apex, that the chord now stood at 37° above the horizon, and had

therefore risen 50°. On the next day similar angular measurements of

the same leaf were made; and at noon the chord stood 36° beneath the

horizon, and 9.30 P.M. 3½° above it, so had risen 39½°. The chief cause

of the rising movement lies in the straightening of the blade, but the

short petiole rises between 4° and 5°. On the third night the chord

stood at 35° above the horizon, and if the leaf occupied the same

position at noon, as on the previous day, it had risen 71°. With older

leaves no such change of curvature could be detected. The plant was

then brought into the house and kept in a north-east room, but at night

there was no change in the curvature of the young leaves; so that

previous exposure to a strong light is apparently requisite for the

periodical change of curvature in the blade, and for the slight rising

of the petiole.

Fig. 110. Cyclamen Persicum: circumnutation of leaf, traced from 6.45

A.M. June 2nd to 6.40 A.M. 5th. Apex of leaf 7 inches from the vertical

glass.

(21.) Wigandia (Hydroleaceae, Fam. 149).—Professor Pfeffer informs us

that the leaves of this plant rise in the evening; but as we do not

know whether or not the rising is great, this species ought perhaps to

be classed amongst sleeping plants.

Fig. 111. Petunia violacea: downward movement and circumnutation of a

very young leaf, traced from 10 A.M. June 2nd to 9.20 A.M. June 6th.

N.B.—At 6.40 A.M. on the 5th it was necessary to move the pot a little,

and a new tracing was begun at the point where two dots are not joined

in the diagram. Apex of leaf 7 inches from the vertical glass. Temp.

generally 17½° C.

(22.) Petunia violacea (Solaneae, Fam. 157).—A very young leaf, only

3/4 inch in length, highly inclined upwards, was observed for four

days. During the whole of this time it bent outwards and downwards, so

as to become more and more nearly horizontal. The strongly marked

zigzag line in the figure on p. 248 (Fig. 111), shows that this was

effected by modified circumnutation; and during the latter part of the

time there was much ordinary circumnutation on a small scale. The

movement in the diagram is magnified between 10 and 11 times. It

exhibits a clear trace of periodicity, as the leaf rose a little each

evening; but this upward tendency appeared to be almost conquered by

the leaf striving to become more and more horizontal as it grew older.

The angles which two older leaves formed together, were measured in the

evening and about noon on 3 successive days, and each night the angle

decreased a little, though irregularly.

Fig. 112. Acanthus mollis: circumnutation of young leaf, traced from

9.20 A.M. June 14th to 8.30 A.M. 16th. Apex of leaf 11 inches from the

vertical glass, so movement considerably magnified. Figure here reduced

to one-half of original scale. Temp. 15°–16½° C.

(23.) Acanthus mollis (Acanthaceae, Fam. 168).—The younger of two

leaves, 2 1/4 inches in length, petiole included, produced by a

seedling plant, was observed during 47 h. Early on each of the three

mornings, the apex of the leaf fell; and it continued to fall till 3

P.M., on the two afternoons when observed. After 3 P.M. it rose

considerably, and continued to rise on the second night until the early

morning. But on the first night it fell instead of rising, and we have

little doubt that this was owing to the leaf being very young and

becoming through epinastic growth more and more horizontal; for it may

be seen in the diagram (Fig. 112), that the leaf stood on a higher

level on the first than on the second day. The leaves of an allied

species (‘A. spinosus’) certainly rose every night; and the rise

between noon and 10.15 P.M., when measured on one occasion, was 10°.

This rise was chiefly

or exclusively due to the straightening of the blade, and not to the

movement of the petiole. We may therefore conclude that the leaves of

Acanthus circumnutate periodically, falling in the morning and rising

in the afternoon and night.

(24.) Cannabis sativa (Cannabineae, Fam. 195).—We have here the rare

case of leaves moving downwards in the evening, but not to a sufficient

degree to be called sleep.[12] In the early morning, or in the latter

part of the night, they move upwards. For instance, all the young

leaves near the summits of several stems stood almost horizontally at 8

A.M. May 29th and at 10.30 P.M. were considerably declined. On a

subsequent day two leaves stood at 2 P.M. at 21° and 12° beneath the

horizon, and at 10 P.M. at 38° beneath it. Two other leaves on a

younger plant were horizontal at 2 P.M., and at 10 P.M. had sunk to 36°

beneath the horizon. With respect to this downward movement of the

leaves, Kraus believes that it is due to their epinastic growth. He

adds, that the leaves are relaxed during the day, and tense at night,

both in sunny and rainy weather.

[12] We were led to observe this plant by Dr. Carl Kraus’ paper,

‘Beiträge zur Kentniss der Bewegungen Wachsender Laubblätter,’ Flora,

1879, p. 66. We regret that we cannot fully understand parts of this

paper.

(25.) Pinus pinaster (Coniferæ, Fam. 223).—The leaves on the summits of

the terminal shoots stand at first in a bundle almost upright, but they

soon diverge and ultimately become almost horizontal. The movements of

a young leaf, nearly one inch in length, on the summit of a seedling

plant only 3 inches high, were traced from the early morning of June

2nd to the evening of the 7th. During these five days the leaf

diverged, and its apex descended at first in an almost straight line;

but during the two latter days it zigzagged so much that it was

evidently circumnutating. The same little plant, when grown to a height

of 5 inches, was again observed during four days. A filament was fixed

transversely to the apex of a leaf, one inch in length, and which had

already diverged considerably from its originally upright position. It

continued to diverge (see A, Fig. 113), and to descend from 11.45 A.M.

July 31st to 6.40 A.M. Aug. 1st. On August 1st it circumnutated about

the same small space, and again descended at night. Next morning the

pot was moved nearly one inch to the right, and a new tracing was begun

(B). From this time, viz., 7 A.M. August 2nd to 8.20 A.M. on the 4th,

the leaf manifestly circumnutated. It does not appear from the diagram

that the leaves move periodically, for the descending course during the

first two nights, was clearly due to epinastic growth, and at the close

of our observations the leaf was not nearly so horizontal as it would

ultimately become.

Fig. 113. Pinus pinaster: circumnutation of young leaf, traced from

11.45 A.M. July 31st to 8.20 A.M. Aug. 4th. At 7 A.M. Aug. 2nd the pot

was moved an inch to one side, so that the tracing consists of two

figures. Apex of leaf 14½ inches from the vertical glass, so movements

much magnified.

Pinus austriaca.—Two leaves, 3 inches in length, but not

quite fully grown, produced by a lateral shoot, on a young tree 3 feet

in height, were observed during 29 h. (July 31st), in the same manner

as the leaves of the previous species. Both these leaves certainly

circumnutated, making within the above period two, or two and a half,

small, irregular ellipses.

(26.) Cycas pectinata (Cycadeæ, Fam. 224).—A young leaf, 11½ inches in

length, of which the leaflets had only recently become uncurled, was

observed during 47 h. 30 m. The main petiole was secured to a stick at

the base of the two terminal leaflets. To one of the latter, 3 3/4

inches in length, a filament was fixed; the leaflet was much bowed

downward, but as the terminal part was upturned, the filament projected

almost horizontally. The leaflet moved (see Fig. 114) largely and

periodically, for it fell until about 7 P.M. and rose during the night,

falling again next morning after 6.40 A.M. The descending lines are in

a marked manner zigzag, and so probably would have been the ascending

lines, if they had been traced throughout the night.

Fig. 114. Cycas pectinata: circumnutation of one of the terminal

leaflets, traced from 8.30 A.M. June 22nd to 8 A.M. June 24th. Apex of

leaflet 7 3/4 inches from the vertical glass, so tracing not greatly

magnified, and here reduced to one-third of original scale; temp.

19°–21° C.

CIRCUMNUTATION OF LEAVES: MONOCOTYLEDONS.

(27.) Canna Warscewiczii (Cannaceae, Fam. 2).—The movements of a young

leaf, 8 inches in length and 3½ in breadth, produced by a vigorous

young plant, were observed during 45 h. 50 m., as shown in Fig. 115.

The pot was slided about an inch to the right on the morning of the

11th, as a single figure would have been too complicated; but the two

figures are continuous in time. The movement is periodical, as the leaf

descended from the early morning until about 5 P.M., and ascended

during the rest of the evening and

part of the night. On the evening of the 11th it circumnutated on a

small scale for some time about the same spot.

Fig. 115. Canna Warscewiczii: circumnutation of leaf, traced (A) from

11.30 A.M. June 10th to 6.40 A.M. 11th; and (B) from 6.40 A.M. 11th to

8.40 A.M. 12th. Apex of leaf 9 inches from the vertical glass.

(28.) Iris pseudo-acorus (Irideae, Fam. 10).—The movements of a young

leaf, rising 13 inches above the water in which the plant grew, were

traced as shown in the figure (Fig. 116), during 27 h. 30 m. It

manifestly circumnutated, though only to a small extent. On the second

morning, between 6.40 A.M. and 2 P.M. (at which latter hour the figure

here given ends), the apex changed its course five times. During the

next 8 h. 40 m. it zigzagged much, and descended as far as the lowest

dot in the figure, making in its course two very small ellipses; but if

these lines had been added to the diagram it would have been too

complex.

Fig. 116. Iris pseudo-acorus: circumnutation of leaf, traced from 10.30

A.M. May 28th to 2 P.M. 29th. Tracing continued to 11 P.M., but not

here copied. Apex of leaf 12 inches beneath the horizontal glass, so

figure considerably magnified. Temp. 15°–16° C.

(29.) Crinum Capense (Amaryllideae, Fam. 11).—The leaves of this plant

are remarkable for their great length and narrowness: one was measured

and found to be 53 inches long and only 1.4 broad at the base. Whilst

quite young they stand up almost vertically to the height of about a

foot; afterwards

their tips begin to bend over, and subsequently hang vertically down,

and thus continue to grow. A rather young leaf was selected, of which

the dependent tapering point was as yet only 5½ inches in length, the

upright basal part being 20 inches high, though this part would

ultimately become shorter by being more bent over. A large bell-glass

was placed over the plant, with a black dot on one side; and by

bringing the dependent apex of the leaf into a line with this dot, the

accompanying figure (Fig. 117) was traced on the other side of the

bell, during 2½ days. During the first day (22nd) the tip travelled

laterally far to the left, perhaps in consequence of the plant having

been disturbed; and the last dot made at 10.30 P.M. on this day is

alone here given. As we see in the figure, there can be no doubt that

the apex of this leaf circumnutated.

Fig. 117. Crinum Capense: circumnutation of dependent tip of young

leaf, traced on a bell-glass, from 10.30 P.M. May 22nd to 10.15 A.M.

25th. Figure not greatly magnified.

A glass filament with little triangles of paper was at the same time

fixed obliquely across the tip of a still younger leaf, which stood

vertically up and was as yet straight. Its movements were traced from 3

P.M. May 22nd to 10.15 A.M. 25th. The leaf was growing rapidly, so that

the apex ascended greatly during this period; as it zigzagged much it

was clearly circumnutating, and it apparently tended to form one

ellipse each day. The lines traced during the night were much more

vertical than those traced during the day; and this indicates that the

tracing would have exhibited a nocturnal rise and a diurnal fall, if

the leaf had not grown so quickly. The movement of this same leaf after

an interval of six days (May 31st), by which time the tip had curved

outwards into a horizontal position,

and had thus made the first step towards becoming dependent, was traced

orthogonically by the aid of a cube of wood (in the manner before

explained); and it was thus ascertained that the actual distance

travelled by the apex, and due to circumnutation, was 3 1/8 inches in

the course of 20½ h. During the next 24 h. it travelled 2½ inches. The

circumnutating movement, therefore, of this young leaf was strongly

marked.

(30.) Pancratium littorale (Amaryllideae).—The movements, much

magnified, of a leaf, 9 inches in length and inclined at about 45°

above the horizon, were traced during two days. On the first day it

changed its course completely, upwards and downwards and laterally, 9

times in 12 h.; and the figure traced apparently represented five

ellipses. On the second day it was observed seldomer, and was therefore

not seen to change its course so often, viz., only 6 times, but in the

same complex manner as before. The movements were small in extent, but

there could be no doubt about the circumnutation of the leaf.

(31.) Imatophyllum vel Clivia (sp.?) (Amaryllideae).—A long glass

filament was fixed to a leaf, and the angle formed by it with the

horizon was measured occasionally during three successive days. It fell

each morning until between 3 and 4 P.M., and rose at night. The

smallest angle at any time above the horizon was 48°, and the largest

50°; so that it rose only 2° at night; but as this was observed each

day, and as similar observations were nightly made on another leaf on a

distinct plant, there can be no doubt that the leaves move

periodically, though to a very small extent. The position of the apex

when it stood highest was .8 of an inch above its lowest point.

(32.) Pistia stratiotes (Aroideae, Fam. 30).—Hofmeister remarks that

the leaves of this floating water-plant are more highly inclined at

night than by day.[13] We therefore fastened a fine glass filament to

the midrib of a moderately young leaf, and on Sept. 19th measured the

angle which it formed with the horizon 14 times between 9 A.M. and

11.50 P.M. The temperature of the hot-house varied during the two days

of observation between 18½° and 23½° C. At 9 A.M. the filament stood at

32° above the horizon; at 3.34 P.M. at 10° and at 11.50 P.M. at 55°;

these two latter angles being the highest and the lowest observed

during the day, showing a difference of 45°. The rising did not become

strongly marked until between

5 and 6 P.M. On the next day the leaf stood at only 10° above the

horizon at 8.25 A.M., and it remained at about 15° till past 3 P.M.; at

5.40 P.M. it was 23°, and at 9.30 P.M. 58°; so that the rise was more

sudden this evening than on the previous one, and the difference in the

angle amounted to 48°. The movement is obviously periodical, and as the

leaf stood on the first night at 55°, and on the second night at 58°

above the horizon, it appeared very steeply inclined. This case, as we

shall see in a future chapter, ought perhaps to have been included

under the head of sleeping plants.

[13] ‘Die Lehre von der Pflanzenzelle,’ 1867, p. 327.

(33.) Pontederia (sp.?) (from the highlands of St. Catharina, Brazil)

(Pontederiaceae, Fam. 46).—A filament was fixed across the apex of a

moderately young leaf, 7½ inches in height, and its movements were

traced during 42½ h. (see Fig. 118). On the first evening, when the

tracing was begun, and during the night, the leaf descended

considerably. On the next morning it ascended in a strongly marked

zigzag line, and descended again in the evening and during the night.

The movement, therefore, seems to be periodic, but some doubt is thrown

on this conclusion, because another leaf, 8 inches in height, appearing

older and standing more highly inclined, behaved differently. During

the first 12 h. it circumnutated over a

small space, but during the night and the whole following day it

ascended in the same general direction; the ascent being effected by

repeated up and down well-pronounced oscillations.

Fig. 118. Pontederia (sp.?): circumnutation of leaf, traced from 4.50

P.M. July 2nd to 10.15 A.M. 4th. Apex of leaf 16½ inches from the

vertical glass, so tracing greatly magnified. Temp. about 17° C., and

therefore rather too low.

CRYPTOGAMS.

(34.) Nephrodium molle (Filices, Fam. 1).—A filament was fixed near the

apex of a young frond of this Fern, 17 inches in height, which was not

as yet fully uncurled; and its movements were traced during 24 h. We

see in Fig. 119 that it plainly circumnutated. The movement was not

greatly magnified as the frond was placed near to the vertical glass,

and would probably have been greater and more rapid had the day been

warmer. For the plant was brought out of a warm greenhouse and observed

under a skylight, where the temperature was between 15° and 16° C. We

have seen in Chap. I. that a frond of this Fern, as yet only slightly

lobed and with a rachis only .23 inch in height, plainly

circumnutated.[14]

[14] Mr. Loomis and Prof. Asa Gray have described (‘Botanical

Gazette,’ 1880, pp. 27, 43), an extremely curious case of movement in

the fronds, but only in the fruiting fronds, of Asplenium trichomanes.

They move almost as rapidly as the little leaflets of Desmodium

gyrans, alternately backwards and forwards through from 20 to 40

degrees, in a plane at right angles to that of the frond. The apex of

the frond describes “a long and very narrow ellipse,” so that it

circumnutates. But the movement differs from ordinary circumnutation

as it occurs only when the plant is exposed to the light; even

artificial light “is sufficient to excite motion for a few minutes.”

Fig. 119. Nephrodium molle: circumnutation of rachis, traced from 9.15

A.M. May 28th to 9 A.M. 29th. Figure here given two-thirds of original

scale.

In the chapter on the Sleep of Plants the conspicuous circumnutation of

Marsilea quadrifoliata (Marsileaceae, Fam. 4) will be described.

It has also been shown in Chap. I. that a very young Selaginella

(Lycopodiaceæ, Fam. 6), only .4 inch in height, plainly circumnutated;

we may therefore conclude that older plants, whilst growing, would do

the same.

(35.) Lunularia vulgaris (Hepaticae, Fam. 11, Muscales).—The earth in

an old flower-pot was coated with this plant, bearing gemmae. A highly

inclined frond, which projected .3 inch above the soil and was .4 inch

in breadth, was selected for observation. A glass hair of extreme

tenuity, .75 inch in length, with its end whitened, was cemented with

shellac to the frond at right angles to its breadth; and a white stick

with a minute black spot was driven into the soil close behind the end

of the hair. The white end could be accurately brought into a line with

the black spot, and dots could thus be successively made on the

vertical glass-plate in front. Any movement of the frond would of

course be exhibited and increased by the long glass hair; and the black

spot was placed so close behind the end of the hair, relatively to the

distance of the glass-plate in front, that the movement of the end was

magnified about 40 times. Nevertheless, we are convinced that our

tracing gives a fairly faithful representation of the movements of the

frond. In the intervals between each observation, the plant was covered

by a small bell-glass. The frond, as already stated,

was highly inclined, and the pot stood in front of a north-east window.

During the five first days the frond moved downwards or became less

inclined; and the long line which was traced was strongly zigzag, with

loops occasionally formed or nearly formed; and this indicated

circumnutation. Whether the sinking was due to epinastic growth, or

apheliotropism, we do not know. As the sinking was slight on the fifth

day, a new tracing was begun on the sixth day (Oct. 25th), and was

continued for 47 h.; it is here given (Fig. 120). Another tracing was

made on the next day (27th) and the frond was found to be still

circumnutating, for during 14 h. 30 m. it changed its course completely

(besides minor changes) 10 times. It was casually observed for two more

days, and was seen to be continually moving.

Fig. 120. Lunularia vulgaris: circumnutation of a frond, traced from 9

A.M. Oct 25th to 8 A.M. 27th.

The lowest members of the vegetable series, the Thallogens, apparently

circumnutate. If an Oscillaria be watched under the microscope, it may

be seen to describe circles about every 40 seconds. After it has bent

to one side, the tip first begins to bend back to the opposite side and

then the whole filament curves over in the same direction.

Hofmeister[15] has given a minute account of the curious, but less

regular though constant, movements of Spirogyra: during 2½ h. the

filament moved 4 times to the left and 3 times to the right, and he

refers to a movement at right angles to the above. The tip moved at the

rate of about 0.1 mm. in five minutes. He compares the movement with

the nutation of the higher plants.[16] We shall hereafter see that

heliotropic movements result from modified circumnutation, and as

unicellular Moulds bend to the light we may infer that they also

circumnutate.

[15] ‘Ueber die Bewegungen der Faden der _Spirogyra princeps:_

Jahreshefte des Vereins für vaterländische Naturkunde in Württemberg,’

1874, p. 211.

[16] Zukal also remarks (as quoted in ‘Journal R. Microscop. Soc.,’

1880, vol. iii. p. 320) that the movements of Spirulina, a member of

the Oscillatorieae, are closely analogous “to the well-known rotation

of growing shoots and tendrils.”

CONCLUDING REMARKS ON THE CIRCUMNUTATION OF LEAVES.

The circumnutating movements of young leaves in 33 genera, belonging to

25 families, widely distributed

amongst ordinary and gymnospermous Dicotyledons and amongst

Monocotyledons, together with several Cryptogams, have now been

described. It would, therefore, not be rash to assume that the growing

leaves of all plants circumnutate, as we have seen reason to conclude

is the case with cotyledons. The seat of movement generally lies in the

petiole, but sometimes both in the petiole and blade, or in the blade

alone. The extent of the movement differed much in different plants;

but the distance passed over was never great, except with Pistia, which

ought perhaps to have been included amongst sleeping plants. The

angular movement of the leaves was only occasionally measured; it

commonly varied from only 2° (and probably even less in some instances)

to about 10°; but it amounted to 23° in the common bean. The movement

is chiefly in a vertical plane, but as the ascending and descending

lines never coincided, there was always some lateral movement, and thus

irregular ellipses were formed. The movement, therefore, deserves to be

called one of circumnutation; for all circumnutating organs tend to

describe ellipses,—that is, growth on one side is succeeded by growth

on nearly but not quite the opposite side. The ellipses, or the zigzag

lines representing drawn-out ellipses, are generally very narrow; yet

with the Camellia, their minor axes were half as long, and with the

Eucalyptus more than half as long as their major axes. In the case of

Cissus, parts of the figure more nearly represented circles than

ellipses. The amount of lateral movement is therefore sometimes

considerable. Moreover, the longer axes of the successively formed

ellipses (as with the Bean, Cissus, and Sea-kale), and in several

instances the zigzag lines representing ellipses, were extended in very

different directions during the same day or on

the next day. The course followed was curvilinear or straight, or

slightly or strongly zigzag, and little loops or triangles were often

formed. A single large irregular ellipse may be described on one day,

and two smaller ones by the same plant on the next day. With Drosera

two, and with Lupinus, Eucalyptus and Pancratium, several were formed

each day.

The oscillatory and jerking movements of the leaves of Dionaea, which

resemble those of the hypocotyl of the cabbage, are highly remarkable,

as seen under the microscope. They continue night and day for some

months, and are displayed by young unexpanded leaves, and by old ones

which have lost their sensibility to a touch, but which, after

absorbing animal matter, close their lobes. We shall hereafter meet

with the same kind of movement in the joints of certain Gramineæ, and

it is probably common to many plants while circumnutating. It is,

therefore, a strange fact that no such movement could be detected in

the tentacles of Drosera rotundifolia, though a member of the same

family with Dionaea; yet the tentacle which was observed was so

sensitive, that it began to curl inwards in 23 seconds after being

touched by a bit of raw meat.

One of the most interesting facts with respect to the circumnutation of

leaves is the periodicity of their movements; for they often, or even

generally, rise a little in the evening and early part of the night,

and sink again on the following morning. Exactly the same phenomenon

was observed in the case of cotyledons. The leaves in 16 genera out of

the 33 which were observed behaved in this manner, as did probably 2

others. Nor must it be supposed that in the remaining 15 genera there

was no periodicity in their movements; for 6 of them were observed

during too short a period for any judgment to be formed on this head,

and 3 were so young that their epinastic growth, which serves to bring

them down into a horizontal position, overpowered every other kind of

movement. In only one genus, Cannabis, did the leaves sink in the

evening, and Kraus attributes this movement to the prepotency of their

epinastic growth. That the periodicity is determined by the daily

alternations of light and darkness there can hardly be a doubt, as will

hereafter be shown. Insectivorous plants are very little affected, as

far as their movements are concerned, by light; and hence probably it

is that their leaves, at least in the cases of Sarracenia, Drosera, and

Dionaea, do not move periodically. The upward movement in the evening

is at first slow, and with different plants begins at very different

hours;—with Glaucium as early as 11 A.M., commonly between 3 and 5

P.M., but sometimes as late as 7 P.M. It should be observed that none

of the leaves described in this chapter (except, as we believe, those

of Lupinus speciosus) possess a pulvinus; for the periodical movements

of leaves thus provided have generally been amplified into so-called

sleep-movements, with which we are not here concerned. The fact of

leaves and cotyledons frequently, or even generally, rising a little in

the evening and sinking in the morning, is of interest as giving the

foundation from which the specialised sleep-movements of many leaves

and cotyledons, not provided with a pulvinus, have been developed. the

above periodicity should be kept in mind, by any one considering the

problem of the horizontal position of leaves and cotyledons during the

day, whilst illuminated from above.