HETEROTAXY.
Under this category are here included a variety of deviations from the
ordinary arrangement and position of parts which cannot conveniently be
classed under the preceding or under other headings. The term heterotaxy
is intended to apply to the production of organs in situations where,
under usual circumstances, they would not be formed. It thus does not
include cases of substitution, where one part is replaced by another, or
more or less metamorphosed, nor cases of multiplication, nor of
prolification which are characterised not only by the production of
members in unwonted situations, but also in unwonted numbers. From the
very nature of the anomalies, and specially from the scanty knowledge we
possess concerning their mode of development, it is not possible to
allocate them in all cases correctly, and moreover many of them might as
well be placed in one group as in another.
=Formation of adventitious roots.=--This is of exceedingly common
occurrence in a vast number of plants, so much so that in most cases it
cannot be considered as in any way abnormal; there are, however, a few
instances where the formation of these organs may be considered to come
within the scope of teratology, or, at least, where their production is
the result of injury or of some unfavorable condition to which the plant
is exposed.
Thus the production of adventitious roots on the stem of the vine is
considered to be due to untoward circumstances impairing the proper
action of the ordinary subterranean roots. So, too, the formation of
roots on the upper portions of stems that are more or less decayed
below, as in old willows, is to be considered as an attempt to obtain
fresh supplies through a more vigorous and healthy channel.
A similar occurrence often arises as a consequence of some injury.
Virgil had this circumstance in view when he wrote
"_Quin et, caudicibus sectis, mirabile dictu,
Truditur e sicco radix oleagina ligno._"--'Georg.' Bk. ii.
I have seen many specimens of adventitious roots produced on the olive
in the way just mentioned.
In the 'Gardeners' Chronicle,' January 8th, 1853, p. 21, is described a
curious formation of roots in the fissure between two divisions of a
laburnum stem. In the same journal, January 1st, 1853, p. 4, Mr. Booth
mentions the case of a Cornish elm, the trunk of which was divided at
the top into two main divisions, and from the force of the wind or from
some other cause the stem was split down for several feet below the
fork. Around the edges of the fracture, layers of new bark were formed,
from which numerous roots issued, some measuring an inch in diameter and
descending into the cleft portion of the tree: similar instances must be
familiar to all observers.
It may happen that these roots sent down into the cavity of a decaying
trunk may, after a time, become completely concealed within it, by the
gradual formation and extension of new wood over the orifice of the
cavity formed by the death and decay of the old wood. Such is presumed
to be the explanation of a specimen of this kind in the possession of
the writer, and taken from a cavity in an apparently solid block of
rosewood; externally there were no marks to indicate the existence of a
central space, but when the block was sawn up for the use of the
cabinet-maker, this root-like structure was found in the centre and
attached to one end of the cavity.
The production of roots which ultimately serve as props to support the
branches, or as buttresses to compensate for the increasing weight of
branches and foliage, is also a familiar occurrence. The huge gnaurs and
burrs met with occasionally on some trees often produce great
quantities, not only of adventitious buds, but of roots also.
[Illustration: FIG. 71.--Production of adventitious roots from leaf
stalk of celery.]
The leaves, equally with the stems, have the power of emitting roots
under certain conditions, as when the leaves are in close contact with
moist soil or as the result of injury. This happens in some plants more
readily than in others--_Bryophyllum calycinum_ is a well-known
instance. Mr. Berkeley has described the formation of roots from the
fractured leaves of celery,[147] and also in a cabbage where a snail
"having gnawed a hole into the middle of a leaf at its junction with the
stem, a fascicle of roots was formed, bursting through the tissue lining
the cavity, and covered with abundant delicate hairs after the fashion
of ordinary radicles."
[Illustration: FIG. 72.--Germinating plant of mango, showing production
of roots from one of the cotyledons (from the Kew Museum).]
The production of adventitious roots is not limited to the ordinary
leaves of the plant, but may be manifested on the cotyledons; thus
Irmisch describes cases of this kind in the cotyledons of _Bunium
creticum_ and _Carum Bulbocastanum_.[148] I have figured and described
an analogous case in the cotyledons of the Mango (fig. 72).[149]
To this formation of adventitious roots the gardener owes the power he
has of propagating plants by cuttings, _i.e._, small portions of the
stem with a bud or buds attached, or in some cases from portions of the
leaves, of the roots themselves, or even of the fruit, as in the case of
the cactus (Baillon). Care also has to be exercised in grafting certain
fruit trees not to allow the grafted portion to be too close to the
ground, else the scion throws out roots into the soil, and the object of
the cultivator is defeated.
[Illustration: FIGS. 73 and 74 show formation of roots from leaves
induced by the art of the gardener.]
Layering is another garden operation dependent on the formation of these
organs, and advantage is also sometimes taken of this tendency of some
plants to produce roots when injured to reduce the dimensions of a plant
when getting too large for the house in which it is growing. By
gradually inducing the production of new roots from the central or upper
portions of the stem, it becomes possible, after a time, to sever the
connection between the original roots and the upper portion of the
trunk, and thus secure a shortened plant.
On the subject of adventitious roots, &c., reference may be
made to Trecul, 'Ann. Sc. Nat.,' 1846, t. v, p. 340, et vi, p.
303. Duchartre, 'Elements de Botanique,' p. 219. Lindley,
'Theory and Practice of Horticulture.' Thomson's 'Gardener's
Assistant,' pp. 374, _et seq._; and any of the ordinary
botanical text-books.
=Formation of adventitious buds on roots.=--One of the characteristics
by which roots are distinguished from stems in a general way consists in
the absence of buds; but, as is well known, they may be formed on the
roots under certain circumstances, and in certain plants, e.g., _Pyrus
Japonica_, _Anemone Japonica_, &c. What are termed suckers, owe their
origin to buds formed in this situation.
If roots be exposed or injured, they will frequently emit buds. The
well-known experiment of Duhamel, in which a willow was placed with the
branches in the soil and the roots in the air, and emitted new buds from
the latter and new roots from the former, depended on this production of
adventitious organs of either kind.
Gardeners often avail themselves of the power that the roots have of
producing buds to propagate plants by cuttings of the roots, but in many
of these cases the organ "parted" or cut is really an underground stem
and not a true root.
M. Claas Mulder has figured and described a case in the turnip-radish of
the unusual formation of a leafy shoot from the root, apparently after
injury.[150] From the figure it appears as if the lower portion of the
root had been split almost to the extremity, while the upper portion
seems to have a central cavity passing through it. From the angle,
formed by the split segments below, proceeds a tuft of leaves, some of
which appear to have traversed the central cavity and to have emerged
from the summit, mingling with the other leaves in that situation. The
production of a flower-bud has even been noticed on the root of a
species of _Impatiens_.
=Formation of shoots beneath the cotyledons.=--The tigellar or axial
portion of the embryo plant, as contrasted with the radicle proper, is
very variously developed in different cases; sometimes it is a mere
"collar" bearing the cotyledons, while at other times it is of
considerable size. Generally it does not give origin to shoots or leaves
other than the seed-leaves, but occasionally shoots may be seen
projecting from it below the level of the cotyledons. This happens
frequently in seedling plants of _Anagallis arvensis_, _Euphorbia_
_peplus_, and other species, _Linaria vulgaris_, some _Umbelliferae_,
&c.[151]
=Adventitious formation of leaves.=--The term phyllomania has been
vaguely applied both to the production of an unwonted number of leaves
and to their development in unusual situations. Under the present
heading the latter class of cases are alone included. The extraordinary
tendency in some Begonias to develop leaves or leafy excrescences from
their surfaces is elsewhere alluded to, and is, in reality, a species of
hypertrophy or over-luxuriant growth.
In some flowers where the inferior ovary is supposed to be, in part at
least, formed by a dilatation of the top of the flower-stalk, leaves
have been met with proceeding from the surface of the ovary or fruit, as
in _Crataegus tanacetifolia_, roses, pears, gooseberries, &c. In a
specimen of _Nymphaea alba_ I have met with scale-like leaves projecting
from the surface of the fruit (or torus?), and which did not appear to
be metamorphosed stamens or styles (fig. 76).
[Illustration: FIG. 75.--Leaf proceeding from hip of the Rose.]
[Illustration: FIG. 76.--Leaves proceeding from the ovary of
_Nymphaea_.]
For other illustrations of increased leaf-formation, see Multiplication
of foliar organs.
[Illustration: FIG. 77.--_Leontodon_. Scape with two leaves; the bracts
of the involucre are also leafy.]
=Production of leaves on a usually leafless inflorescence.=--The
development of the bracts of an inflorescence to such an extent that
they resemble ordinary leaves is elsewhere alluded to as of common
occurrence. It happens far less frequently that leaves are developed on
an inflorescence usually destitute of them, without any metamorphosis or
substitution, and without any formation of adventitious buds, such as
happens in prolification. Such a partial change from a floriferous to a
foliiferous branch may be seen in a specimen of _Sambucus nigra_ in the
Smithian herbarium in the Linnean Society, where the ultimate branches
of the cyme bear small leaves. My attention was directed to this
specimen by the Rev. W. Newbould.
Jacquin figures an analogous case in _Sempervivum sediforme_,[152] in
which the branches of the inflorescence were prolonged into leafy
shoots.
Sometimes from the side of a flower-stalk or scape, which usually does
not bear leaves, those organs are produced. The common dandelion,
_Taraxacum_, sometimes offers an illustration of this, and also the
daisy (_Bellis_).[153] In a specimen of fasciated cowslip given me by
Mr. Edgeworth there was a similar formation of leaves on the flattened
stalk.
=Production of leaves or scales in place of flower-buds.=--The position
of the leaf and of the flower-buds respectively is, in most plants, well
defined, but occasionally it happens that the former is formed where,
under ordinary circumstances, the latter organ should be. This may
happen without the formation of any transitional organs between the two,
and without actual increase in the number of the buds. Where there is
evidently a passage from leaf-bud to flower-bud, or _vice versa_, the
case would be one of metamorphy. If the number of buds be augmented, or
they be mixed with the flower-buds, then it would be referable to leafy
prolification of the inflorescence. There remains a class of cases
wherein there is a complete substitution of one structure for the other,
it may be without the slightest indication of transition between the
two, and without any admixture of leaf-buds among flower-buds, or any
absolute increase in the number of organs, as in Prolification. Such a
case is represented in fig. 78, which shows a portion of the stem of a
species of _Valeriana_, bearing at the summit, not an inflorescence, but
a tuft of leaves without the slightest indication of flowers.
Drs. Hooker and Thomson relate that in Northern India the flowers of
_Anemone rivularis_ are very generally absent, and their place supplied
by tufts or umbels of leaves.[154] In the collection of the late Mr. N.
B. Ward was a specimen of lupin in which the flowers were all absent,
and their place supplied by tufts of leaves.
[Illustration: FIG. 78.--Tuft of leaves replacing the inflorescence in a
species of _Valeriana_.]
A similar appearance has been noticed in _Compositae_, and I owe to the
kindness of Professor Oliver the communication of a specimen of a
species of _Bidens_ from Peru, in which the capitula, instead of
consisting of florets, as usual, contained tufts of linear ciliolated
bracts within the involucre, without a trace of flowers. In the eleventh
volume of the 'Linnaea,' 1837, p. 301, Von Cesati figures and describes
an analogous case in _Carduus crispus_. The same author[1] records a
similar instance in the umbel of _Seseli coloratum_, where the place of
the flowers was occupied by stalked tufts of leaves. In the 'Gardeners'
Chronicle,' October 6th, 1860, p. 894, is mentioned an instance where
the blossoms of the pea were entirely absent, and their place supplied
by accumulations of small, ovate, green scales, thus presenting an
appearance similar to that brought about by the inordinate
multiplication of the sepals in the "wheat-ear carnation," and in the
Sweet William, and not unlike the condition met with in _Bryophyllum
proliferum_. In _Digitalis purpurea_ a similar anomaly is sometimes met
with.
In the apple I have observed leafy shoots bearing terminal tufts of
leaves where the flower should have been, so that what, under ordinary
circumstances would be a corymb of flowers, is here represented by a
series of tufts of leaves. In the cultivated azaleas also, leafy shoots
occupying the position of the flower may occasionally be met with.
In _Bouchea hyderabadensis_ I have seen the inflorescence more than
usually branched and covered with little tufts of bracts, without a
trace of true flower. A similar condition seems not infrequent in
_Gentiana Amarella_, as I have not only met with the plant myself in
this condition, but have been favoured with specimens by Mr. Pamplin,
Mr. Darwin, and others. In _Phyteuma spicatum_ an analogous appearance
has been recorded.
Among Griffith's collections from Affghanistan is a species of willow
(_Salix_) in which the inflorescence replaced by a much branched
panicle, bearing a quantity of minute bracts, in the axils of which
nestle numerous small buds. In another specimen the inflorescence
preserves its usual catkin-like shape, but the flowers are replaced by
little tufts of leaves. M. Germain de Saint Pierre mentions a case
wherein the flowers of _Alisma parnassifolia_ were completely replaced
by leaf-buds.[155]
[Illustration: FIG. 79.--Spikelets of _Willedenovia_, composed entirely
of scales to the exclusion of flowers.]
[Illustration: FIG. 80.--Rose Willow, _Salix_, sp.]
Here, also, may be mentioned the curious aggregations of scales which
occur in some grasses, in _Restiaceae_, _Juncaceae_, and other orders, in
which the inflorescence is made up of collections of scales or bracts
with no trace of floral structure. Fig. 79 shows this in a species of
_Willdenovia_, and a very good example is figured in a bamboo,
_Pseudostachyum polymorphum_, by General Munro.[156]
"Rose willows" (fig. 80) owe their peculiar appearance to a similar
cause, the scales of the catkin being here replaced by closely crowded
leaves. These aggregations of scales or leaves are not confined to the
inflorescence, but may be found in other parts of the plant, and may be
frequently met with in the willow, birch, oak, &c., generally as the
result of insect puncture. On the other hand, the production of leaves
or leaf-buds in place of flowers is, as is well known, generally the
consequence of an excess of nutrition, and of the continuance rather
than of the arrest of vegetative development.[157] It has even been
asserted that a flower-bud may be transformed into a leaf-bud by
removing the pistil at a very early stage of development, but this
statement requires further confirmation.[158]
=Viviparous plants.=--The spikelets of certain grasses are frequently
found with some of their constituent parts completely replaced by
leaves, like those of the stem, while the true flowers are usually
entirely absent. A shoot, in fact, is formed in place of a series of
flowers. In these cases it generally happens that the outermost glumes
are changed, sometimes, however, even the outer and inner paleae are
wholly unchanged, while there is no trace of squamulae or of stamens and
pistils within them, but in their place is a small shoot with miniature
leaves arranged in the ordinary manner.
The grasses most commonly affected in this manner are _Dactylis
glomerata!_, _Poa bulbosa!_, _Poa annua!_, _P. trivialis!_,
_pratensis!_, _alpina!_, _angustifolia_, and _laxa_, _Cynosurus
cristatus_, _Festuca nemoralis_, _F. ovina!_, _Glyceria fluitans!_, _Gl.
aquatica_, _Aira alpina!_, _caespitosa!_, _Phleum phalaroides_, _Lolium
perenne!_, _Alopecurus pratensis!_, _Agrostis alba_, _Holcus mollis!_
[Illustration: FIG. 81.--Portion of panicle of _Aira vivipara_ and
separate floret.]
From an examination of the structure of viviparous grasses Von Mohl was
led to the conclusion that the lower palea is to be considered as a
bract, and not a perianthial leaf, because the base of the palea
surrounds the stem or axis of the spikelet entirely, and both its
margins cohere towards its lower extremity.[159]
A similar condition occurs not infrequently in _Polygonum viviparum_,
and in _Juncaceae_, _Cyperaceae_, &c.
In the genus _Allium_ an analogous formation of little buds or bulbils
takes place in lieu of flowers; this is specially the case with _A.
vineale_, the flowers of which are rarely seen.
Other illustrations of a similar character, where the adventitious
leaf-buds are mixed in amongst the flower-buds, are cited under the head
of Prolification of the Inflorescence.
=Formation of buds on leaves.=--The formation of little bulbs upon the
surfaces or edges of leaves, forming what are called viviparous leaves,
has long been familiar to botanists amongst Alliums. Professor Alexander
Braun,[160] who has paid much attention to this subject, divides cases
of this kind according to the position of the buds; thus, for instance,
they are sometimes formed upon the upper portion of the leaf or petiole,
as in many ferns, in _Nymphaea guineensis_, some _Arads_, &c. The same
condition has been met with as a teratological occurrence in the leaves
of _Cardamine pratensis_, _Hyacinthus Pouzolzii_, _Drosera
intermedia_,[161] _Arabis pumila_, _Chelidonium majus_, _Chirita
sinensis_,[162] _Episcia bicolor_,[163] _Zamia_, &c.[164] Many species
of _Begonia_ possess the power of emitting buds from the petioles and
veins of the leaf; the little ramenta or scales which so plentifully
beset the surface of some of these plants likewise, in some instances,
pass gradually into leaves. _B. phyllomaniaca_, Mart., is the species
best known as manifesting this tendency, but others have it also.[165]
Buds are also very often formed upon the margins of the leaf, the best
known instance of which occurs in _Bryophyllum calycinum_;
Weinmann[166] figures an instance of this kind in _Alchemilla minima_,
or they may occur upon the lower surface of the leaf, as in
_Ornithogalum scilloides_ and _longe-bracteatum_. M. Duchartre[167]
mentions a case in the tomato in which the leaves gave origin to small
leaf-bearing branches, which, of course, must have originated from buds,
just in the same way as in the _Drosera_ before mentioned.
[Illustration: FIG. 82.--Formation of shoot on leaf of _Episcia
bicolor_.]
Gardeners occasionally avail themselves of this formation of buds from
leaves to propagate plants, _e.g._ _Hoya_, _Gesnera_, _Gloxinia_, &c.
=Formation of buds in the pith.=--This is said to be a normal condition
in the curious _Stangeria paradoxa_,[168] and Mr. Berkeley records an
instance of this in sea-kale[169] (fig. 83) where the crown had been
injured, and buds were seen sprouting from its centre.
[Illustration: FIG. 83.--Adventitious buds in sea kale.]
[Illustration: FIG. 84.--Hyacinth bulb cut across to induce the
formation of new bulbs.]
[Illustration: FIG. 85.--Showing the formation of new bulbs on the cut
edges of an old hyacinth bulb.]
It will be remarked that the adventitious production of buds, like that
of roots, is very often consequent on decay or injury. The Dutch
bulb-growers have availed themselves of this latter circumstance in the
propagation of hyacinths. Mr. Fortune, who published some articles on
this subject in the 'Gardener's Chronicle,'[170] describes two special
modes as adopted by these skilful horticulturists--the one to make two
or three deep cuts at the base of the bulb, destroying the nascent
flower-stalk when, after a time, small bulbs are formed along the edges
of the cut surfaces (figs. 84, 85). The other method is effected by
scooping out the interior of the base of the bulb, thus leaving exposed
the cut ends of the sheathing leaves arranged concentrically; along
these lines the new bulbs are, after some time, formed in great numbers
(fig. 86).
[Illustration: FIG. 86.--Showing the production of small bulbs on the
inner surface of the scooped-out bulb of hyacinth.]
For the formation of supernumerary leaves on the surface of the normal
one, see Multiplication and Hypertrophy.
=Production of gemmae in place of spores.=--An instance of this is
recorded by Dr. Montagne[171] in the case of a moss, _Encamptodon
perichaetialis_, in which, in the interior of the capsule, in lieu of
spores numerous minute gemmae of the same nature as those in the cup of
_Marchantia_ were seen.
=Formation of flowers on leaves.=--It is very doubtful whether a
flower-bud has ever been found actually on a leaf. Mere adhesion of the
pedicels of the leaf, such as happens in _Ruscus_, in _Helwingia_,
_Erythrochiton hypophyllanthus_, and a few other plants, is, of course,
not really to be considered in the light of an actual growth from the
leaf, and it is very doubtful in the present state of our knowledge
whether the case of the Nepaul barley should find a place here, but for
convenience sake it is placed in this section, as it is uncertain at
present where it properly belongs.
[Illustration: FIG. 87.--Three-lobed end of outer palea of Nepaul barley
bearing supplementary florets.]
[Illustration: FIG. 88.--Three spikelets of Nepaul barley.]
[Illustration: FIG. 89.--Lip of outer palea of Nepaul barley.]
[Illustration: FIG. 90.--Supplementary rachillus or outer palea of
Nepaul barley bearing florets.]
[Illustration: FIG. 91.--Diagram showing arrangement of supplementary
rachillus and florets.]
[Illustration: FIG. 92.--Supplementary floret of Nepaul barley; palea
removed.]
This curious plant has been described and figured by Irmisch in the
13th volume of the 'Linnaea,' p. 124, t. iv; also by Professor Henslow,
'Hooker's Journal of Botany,' 1849, vol. i, p. 33, tabs. 2, 3. The lower
palea of this plant forms an inverted flower-bud upon its midrib. In
some fresh specimens which I have lately examined I find the structure
to be as follows:--On each notch of the rachis there are three spikelets
(fig. 88), each one-flowered, and each provided with two linear glumes;
the outer palea in all cases is three-lobed at the summit, the central
lobe being oblong and hollow, forming a kind of hood (figs. 87-89), and
covered with hairs, which are directed downwards towards the centre of
the plant. The two lateral lobes are more pointed than the central one;
like it they are provided with hairs, but the hairs, in this case, are
turned away from the centre of the plant. The cavity of the side lobes
is generally empty, but that of the central lobe is occupied by a very
slender stalk, which is apparently the termination of the midrib, but
which is bent inwards at an acute angle, so as to occupy the hollow
space (figs. 90-91). On this slender axis are developed two florets,
more or less imperfect in their structure. Only one of the florets that
I have seen contained a perfect ovary. The tips of the lateral lobes of
the paleae in the primary flower are sometimes extended into a long awn.
A similar awn may also be occasionally found on the tips of the paleae of
the rudimentary florets. The occurrence of an adventitious axial
structure with rudimentary flowers has been adduced in support of the
opinion that the lower paleae is, at least so far as its midrib is
concerned, an axial rather than a foliar structure, but in the present
uncertain state of our knowledge as to the morphology of grasses it is
hazardous to risk any explanation founded on so exceptional a case as
that of the Nepaul barley.[172]
=Production of flower-buds in place of leaf-buds.=--Under natural
circumstances this does not appear to be of so common occurrence as the
change above alluded to, but by the art of the gardener the change is
often effected. In rhododendrons and in peach trees and roses I have met
with this change occurring without human agency. The means adopted by
the gardener are such as check the luxuriance of the leaf-shoots,[173]
and this is effected in various ways, as by continuous "pinching" or
removal of the leaf-buds, by pruning, ringing the bark, confining the
roots, limiting the supply of nutriment, and other means all based on
the same principle. Some of the Cape bulbs (_Cyrtanthus_) are known not
to produce their flowers till their leaves have received, in some
manner, a check. Fires which often destroy the herbage thus have the
effect of throwing the plant into bloom. A very remarkable instance is
recorded of the production of flower-buds after an injury to the
leaf-buds in the 'Bulletin of the Botanical Society of France,' vol. ix,
p. 146. It appears that during the war of the French against the Arabs
in Algiers, the latter planted several hundreds of Agaves with a view to
obstruct the passage of the French cavalry. The soldiers hacked these
plants with their sabres, and cut out the central tuft of leaves, or the
heart, as gardeners call it. The following season almost every one of
these Agaves sent up their large handsome flower-spikes. It is well
known that, under ordinary circumstances, these plants do not flower
except at long intervals of time.
=Presence of flowers on spines.=--That the spine, as a contracted
branch, should occasionally produce flowers is not to be wondered at,
though the occurrence is by no means common. M. Baillon showed at a
meeting of the Botanical Society of France ('Bulletin,' vol. v, 1858, p.
316) a branched spine of _Gleditschia_ bearing a flower at the end of
each of the sub divisions. This was, therefore, strictly analogous with
those cases in which the peduncle is normally spiney.
=Formation of flower-bud on the petals.=--An instance of this, it is
believed, the only one on record, is cited in the 'Gardeners' Chronicle'
for 1865, p. 760, by the Rev. M. J. Berkeley, who describes the
formation of a flower-bud on the surface of a petal of _Clarkia
elegans_. Reasoning from analogy there seems no reason why buds should
not be formed on the petals as well as on the leaves.
=Formation of buds on fruits.=--This is a point of some moment with
reference to the share which the axis takes in the production of
"inferior" fruits. A very frequent malformation in pears is one wherein
a second pear proceeds from the centre of the first, and even a third
from the centre of the second.[174] Pears are occasionally also observed
arising either from the axils of the sepals of the primary pear or from
the axil of leaves originating on the outer surface of the fruits--using
the term fruit in its popular sense. These cases afford strong
confirmation of the view that the outer portion of the so-called fruit
in these plants is rather to be considered as an expansion and
hollowing-out of the flower-stalk, than as formed from the calyx-tube.
It is noteworthy that the true carpels and seeds are frequently entirely
absent in these cases.[175] Further reference to these fruits will be
made under the head of Hypertrophy.
M. Trecul has described and figured an instance in a species of
_Prismatocarpus_, in which a second flower proceeded from the axil of a
bract attached to the side of the fruit of the first flower.[176] A
similar growth was observed in the fruit of _Philadelphus speciosus_ by
M. A. Gris, who observed that the so-called calyx-tube was provided with
two small bracts, from the axil of one of which proceeded a small
flower-bud.[177]
[Illustration: FIG. 93.--Small buds projecting from the edges of the
fruit in _Opuntia_.]
The fruits of _Opuntia Salmiana_, _O. fragilis_,[178] _O. monacantha_,
and of some species of _Echinocactus_, have been observed to form small
fruit-like branches around their summits. M. Napoleon Doumet describes
the fruit as ripening as usual, but as being destitute of seeds in the
interior; after a little while the fruit begins to wither, and then a
circle of small buds, like those of the stem, may be seen at the top of
the fruit, each bud springing from the axil of a little tuft of wool and
spines found on the fruit. These little buds elongate into long shoots,
produce flowers the following year, which flowers exhibit the same
peculiarity. Gasparini and Tenore are said to have recorded the same
fact as long since as 1832. The specimen from which the figure (fig. 93)
was taken produced its fruits in the Royal Gardens at Kew, and is now
preserved in the museum of that establishment. The adventitious growth
in these cases appears to arise from the tufts of spines, which, it has
been suggested, are the homologues of the sepals. There can, however, be
little doubt that the outer and lower portion of the fruit of _Opuntia_
and its allies is a dilatation of the flower-stalk. This is borne out by
the fruits of _Pereskia_, which bear leaves on their surface arranged
spirally; indeed, the fruits of _Pereskia Bleo_ are mentioned as
producing buds from their summits, in the same way as the _Opuntia_
just cited. _P. Bleo_ is said, by M. Delavaud,[179] to present this
anomaly as a constant occurrence. On the summit of the primary fruit,
arising apparently from the axils of the sepals, or of small leafy
bracts in that situation, are a series of fruit-like branches, which, in
their turn, are surmounted by others, even to the fourth generation.
The fruits of _Tetragonia expansa_ frequently have attached to their
side a secondary flower or fruit in such a position as to lead to the
inference that it springs from the upper portion of the peduncle which
is dilated to invest the true carpels. In other instances it is due to
an adhesion of the pedicel to the side of the fruit. In either case the
production of an adventitious bud might be considered as an illustration
of prolification of the inflorescence, though not as was supposed by
Moquin and others of axillary prolification.[180]
Buds have also been produced artificially on the surface of some of the
fruits in the construction of which the axis is supposed to share; thus,
the unripe fruits of some species of _Lecythis_ were stated by Von
Martius, at a meeting of the German Naturalists at Carlsruhe, to produce
buds when placed in the earth. The fruit of these plants is probably of
the same nature as that of the _Pomaceae_, and Baillon[181] succeeded in
producing buds on the surface of the inferior ovary of _Jussiaea_.
Some of the cases just mentioned have been considered to be instances of
prolification of the fruit, but the fruit has little to do with the
appearances in question.
=Formation of adventitious flowers and fruits within the ovary.=--This
generally arises either from substitution of a flower-bud for an ovule
or from prolification; there are certain cases, however, where the new
growth seems not to be either due to metamorphosis or to prolification
strictly.
The cut, fig. 94, represents a case where, in the dilated upper portion
of the ovary of _Sinapis arvensis_, two flower-buds were found
projecting from a raised central line, corresponding, as it would seem,
to the midrib, and not to the margins of the carpel. Similar cases have
occurred in _Nasturtium amphibium_, _Brassica Rapa_, and _Passiflora
quadrangularis_.
[Illustration: FIG. 94.--Distended pod of _Sinapis arvensis_ bearing in
the interior stalked flower buds.]
In Bromfield's 'Flora Vectensis,' p. 35, the following account is given
of an abnormal development in _Cardamine pratensis_: "On the lower part
of the corymb were several seed vessels on pedicels changed from their
usual linear to an ovate elliptical figure, so as to resemble a
silicula. These, on being opened, were found to contain petals of the
usual colour, which in the pods above had burst from their confinement
and appeared as semi-double flowers; the valves of the pod answering to
the true calyx. * * * From their verticillate arrangement it is evident
that these petaloid expansions were not transformed seeds, but simply a
development of the common axis within the ovary into an abortive whorl
of floral organs, besides which there were evident rudiments both of
stamens and germens in the centre of the bundle." Baillon[182] also
records a case of the same nature in _Sinapis arvensis_.
[Illustration: FIG. 94*.--Portion of the interior of the silicle in
_Cheiranthus Cheiri_, showing adventitious pod in the place of an
ovule.]
[Illustration: FIG. 95.--Adventitious pod from fig. 94, enlarged.]
Here, too, may also be mentioned the presence of an adventitious siliqua
within the ordinary one attached along the same line as the ovules, and
partially divided by a replum into two cavities. In this case there was
nothing to indicate the presence of floral envelopes (figs. 94, 95). A
similar occurrence has been brought under my notice in some grapes which
were observed to be cracking before they were perfectly ripe, and in
which adventitious fruits were found within the parent grape, occupying
the position of seeds (figs. 96, 97).
Similar anomalous growths are noticed under the heads of Substitution
and Prolification.
=Formation of stamens within the cavity of the ovary.=--The only
instance of this that has come under the author's observation occurred
in some flowers of _Baeckea diosmaefolia_, Rudge, for an examination of
which he is indebted to Mr. Bentham.
[Illustration: FIG. 96.--Section of Barbarossa grape showing
adventitious grape in the position of a seed.]
[Illustration: FIG. 97.--Grape with supplementary fruit in the interior]
In the normal flower there is a turbinate hollow calyx, whose limb is
divided into five serrated lobes; alternating with these latter, and
springing from the throat of the calyx, are the petals. Originating from
the same annular disk as the petals are the stamens, seven or eight in
number. The ovary is partially adherent, is surmounted by a style, and
has two or three loculi with an axile placenta, to which several small
curved ovules are attached. The malformed flowers did not present
anything peculiar in their outer parts, nor did the ovary, partially
immersed within the expanded top of the flower-stalk and the calyx-tube,
which is continuous with that organ, show externally any indication of
the change within. On cutting it across, however, in any direction,
numerous perfect stamens (filaments and anthers) were seen projecting
from the walls of the cavity (fig. 98). In most of the flowers the ovary
was one-celled; but in a few there was the usual axile placenta; yet
even in these latter cases the stamens originated from the walls of the
cavity, and not from the placenta. The stamens presented different
degrees of development; in some cases they were fully formed, the
anther-lobes open, and the pollen exposed; while in other instances the
filaments were involute or circinate, just as the ordinary stamens are
in the unexpanded flower-bud. In some cases imperfect stamens were
found, mere barren filaments, with or without rudimentary anthers at the
top. In no instance was there a perfect ovule, or, indeed, any trace of
ovules. The stamens appeared to be arranged irregularly on the walls of
the ovarian cavity; and while they were certainly more numerous at the
lower portion (that now generally considered to be formed by the
cup-like end of the pedicel), they were not wanting in the upper half of
the ovary (or that which is probably formed from the carpellary leaves).
[Illustration: FIG. 98.--1. Vertical section of flower of _Baeckea
diosmaefolia_, showing stamens within the ovary; magnified ten times. 2.
Transverse section of ovary. 3. Stamen. 4. Imperfect stamen.]
This case differs from most that have been recorded, and in which there
has been a more or less complete substitution of anther for carpel, or
where the tissues of the carpel have produced pollen, and so taken upon
themselves the appearance and functions of anthers. Instances of this
latter kind are not uncommon; but in the _Baeckea_ there were perfect
stamens proceeding from perfect and completely closed ovaries.
Moquin-Tandon[183] cites from Agardh an instance which seems more
closely to resemble the state of things in the _Baeckea_, and which
occurred in a double hyacinth, wherein both anthers and ovules were
borne on the same placenta. Probably, though the fact is not stated, the
ovary of the hyacinth was open; and we are told that the flower was
double--that it was, in fact, modified and changed in more organs than
one; while in the _Baeckea_ nothing at all unusual was observed till the
ovary was cut open. The style was present even in those flowers where
there was no axile placenta; hence in these cases it could not be, as
Lindley stated it to be in the closely allied _Babingtonia_, a
prolongation of the placenta.[184]
=Formation of pollen within the ovules.=--This has now been recorded in
two instances by Mr. S. J. A. Salter in _Passiflora caerulea_ and in _P.
palmata_,[185] and by the author in _Rosa arvensis_.[186]
[Illustration: FIG. 99.--Pollen within the ovule of _Passiflora_ (after
Salter).]
In the case of the passion-flower there were various malformations in
the ovaries, which were all more or less split open at the distal end,
indicating a tendency towards dialysis. The pollen-bearing ovules were
borne on the edges of these ovaries, and presented various intermediate
conditions between anthers and ovules, commencing at the distal
extremity of the carpel with a bi-lobed anther, and passing in series to
the base of the ovary, an antheroid body of ovule-like form, a modified
ovule containing pollen, an ovule departing from a perfectly natural
condition only in the development of a few grains of pollen in its
nucleus, and, finally, a perfect, normal ovule.
In the flowers of the Rose the stamens exhibited almost every
conceivable gradation between their ordinary form and that of the
carpels, while some of the ovules contained pollen in greater or less
abundance. Speaking generally, the most common state of things in these
flowers was the occurrence on the throat of the calyx, in the position
ordinarily occupied by the stamens, and sometimes mingled with those
organs, of twisted, ribbon-like filaments, which bore about the centre
one or more pendulous, anatropous ovules on their margins. Immediately
above the latter organs were the anther-lobes, more or less perfectly
developed, and surmounting these a long style, terminating in a fringed,
funnel-shaped stigma. Sometimes the ovules were perfect, at other times
the nucleus protruded through the foramen, while in a third set the
nucleus was included within the tegument, the ovules having in all
respects their natural external conformation, containing, however, not
only pollen-grains, but also a layer of those peculiar spheroidal cells,
including a fibrous deposit, which are among the normal constituents of
the anther. In one case, where the coat of the ovule was imperfect, and
allowed the nucleus to protrude, the pollen was evidently contained
within the central mass of the structure. In this instance the fibrous
cells were not detected, these being only found in cases where the
investment of the ovule was perfect; and hence it seems likely that the
fibrous cells were part of the coat of the ovule, while the pollen was
formed within the nucleus. In no case was any trace of embryo sac to be
seen.
The main interest, as Mr. Salter remarks, in these cases is
physiological; so far as structure alone is concerned, there does not
appear any reason why pollen-grains should not be developed in any
portion of the plant; the mother cells in which the pollen is formed not
differing, to all outward appearance, from any other cells, unless it be
in size.
The fundamental unity of construction in all the organs of plants could
hardly be better illustrated than by these cases; while, in spite of
their exceptional nature, they must be of great interest
physiologically, as showing the wide limits of possible variation which
thus may even involve the sex, "for an ovule to develop pollen within
its interior," says Mr. Salter, "is equivalent to an ovum in an animal
being converted into a capsule of spermatozoa. It is a conversion of
germ into sperm, the most complete violation of individuality and unity
of sex. * * * * The occurrence of an antheroid ovule and a normal ovule
on the same carpellary leaf realises the simplest and the most absolute
form of hermaphroditism."
It must, however, be remarked that the term substitution would be
preferable to conversion. There is, at present, no evidence to show that
the germinal vesicles were present in these cases; on the other hand, it
seems most probable that they were not, so that the presence of the
pollen-cells must be considered as simply adventitious. It can hardly be
that they were, in the first instance, germinal vesicles, which, in
course of time, became so modified as to assume the appearance of
pollen-grains. Between the nucleus of the ovule and the tubercle of
cellular tissue constituting the primordial anther, there is little or
no difference, so that it may be said that, for a time, there is no
distinction of sex in the nascent flower, but as development goes on,
the difference becomes perceptible. It cannot at present be stated what
precise circumstances induce the one mass to form mother-cells and
pollen-grains, and the other to develop an embryo sac and germinal
vesicles. Position and external circumstances may have some indirect
effect, and it may, perhaps, be significant that in all the instances of
polliniferous ovules, the ovular structures have been exposed on an open
carpel or otherwise, in place of being confined within the cavity of a
closed ovary, as under ordinary circumstances. Even among Conifers the
ovuligerous scales are so closely packed that there is little or no
exposure of the ovules. But, apart from all speculative notions as to
the relation between the structure and functions of the anther and of
the ovule respectively, and of the possibility or the reverse of
parthenogenesis, it will clearly be necessary in any future alleged
occurrence of the latter phenomenon to ascertain whether any or all of
the apparent ovules are, or are not, anthers in disguise.
=Homomorphic flowers of "Compositae."=--In a large section of the
_Compositae_ there is, as is well known, a distinction between the
florets of the "disc" and those of the "ray," the latter being ligulate,
the former tubular.
In what are erroneously called double flowers in this order, _e.g._ in
the Chrysanthemum, Dahlia, &c. &c., the florets are all ligulate. This
change is sometimes classed with peloria, but there is no abnormal
regularity in these cases. On the other hand, were the ligulate florets
to be all replaced by tubular ones, the term peloria would be more
strictly applicable. It will be remembered that in the sub-order
_Liguliflorae_, the florets are naturally all ligulate, so that the
change above mentioned is not in itself a very grave one.
=Heterotaxy affecting the inflorescence.=--Under the head of
Prolification, Heterogamy, &c., various deviations from the normal
inflorescence are alluded to. In this place, therefore, it is only
necessary to mention certain rare deviations from the customary
arrangement of the inflorescence, such as the change from a definite
centrifugal form of inflorescence to an indefinite centripetal one. This
occurs occasionally in roses, where the shoot, instead of terminating in
a flower-bud, lengthens and bears the flower-bud on its sides as in a
raceme.
In the hyacinth, the inflorescence of which is properly indefinite, the
terminal flower may frequently be found to expand first, though in order
of development it may have been the last formed.
It occasionally happens that certain plants will, contrary to their
usual custom, bloom twice in the same season; this usually arises from
the premature development of buds which, under ordinary circumstances,
would not unfold till the following spring. In these instances of what
the French term "fleuraison anticipee," the position of inflorescence is
not changed, but there are other cases where the position of the
inflorescence is altered, as in the laburnum, where, in some seasons,
racemes may be seen springing from short lateral "spurs" along the sides
of the branches, as well as from the extremities of long shoots.
Of a similar nature are those cases wherein stems or branches usually
sterile become fertile; this happens in _Equisetaceae_,[187] in
_Restiaceae_, and other orders. In the equisetums, the condition in
question has been specially noticed to occur after prolonged drought.
_Equisetaceae_ are likewise subject to an anomaly called by Duval Jouve
interruption of the spike, and wherein the scales bearing the spore
cases are separated by whorls of branches instead of forming one compact
unbroken spike as usual.
This alternation of the organs of vegetation and reproduction may also
be seen occasionally in _Typha_, and other plants.
Kirschleger describes a case in which the male catkins of _Salix
cinerea_ were placed at the ends of the branches instead of being
lateral productions; moreover the usual articulation was not formed, so
that the catkin was persistent instead of deciduous.[188]
=Supra-soriferous ferns.=--In the great majority of ferns the sori or
clusters of spore cases are placed on the under surface of the fronds;
nevertheless, a few cases are on record where the fructification is
produced on the upper as well as on the lower surface, and sometimes
abundantly so. This occasionally happens from the elongation of the
normally placed sorus, which thus extends to the margin, and returns on
the upper side, when the sori chance to be placed opposite to the
marginal crenatures. But it is also frequently the case that the sori
are produced on the upper side, distinctly within the margin, and where
there are no corresponding sori beneath. Those varieties which have the
margin crenated or lobed seem most liable to assume this abnormal
supra-soriferous condition. Among the ferns in which this condition has
been observed are the following: _Scolopendrium vulgare_, _Polypodium
anomalum_, Hook., _Asplenium Trichomanes_, _Cionidium Moorei_.[189]
FOOTNOTES:
[147] 'Gard. Chron.' 1852, p. 51.
[148] 'Flora.' 1858, pp. 32-42.
[149] 'Journ. Linn. Soc.,' vol. vi; "Botany," 1862, p. 24.
[150] 'Tijdschrift voor Natuur. Geschied,' 1836, vol. iii, tab. vii, p.
171.
[151] Roeper, 'Enum. Euphorb.,' p. 19. Bernhardi, 'Linnaea,' vii, p.
561, tab. xiv, f. 1. Wydler, "Subcotyled. sprossbildung," 'Flora,' 1850,
p. 337. Hooker, 'Trans. Linn. Soc.,' vol. xxiv, p. 20 (_Welwitschia_).
[152] 'Misc. Austriac. ad Bot.,' vol. i, p. 133, t. 5.
[153] See also Carriere, 'Revue Horticole,' 1866, p. 442; and as to
pears, Radlkofer in 'Bericht ueber die Thaetigkert der Baierischen
Gartenbau Gesellschaft,' 1862, p. 74, t. i.
[154] 'Flora Indica,' p. 23.
[155] 'Bull. Soc. Bot. Fr.,' 1856, p. 53.
[156] 'Trans. Linn. Soc.' xxvi, p. 142, tab. iv, B.
[157] "Si arbusculam, quae in olla antea posita, quotannis floruit et
fructus protulit, deinde deponamus in uberiori terra calidi caldarii,
proferet illa per plures annos multos ac frondosos ramos, sine ullo
fructu. Id quod argumento est, folia inde crescere, unde prius enati
sunt flores; quemadmodum vicissim, quod in folia nunc succrescit, id,
natura ita moderante, in flores mutatur, si eadem arbor iterum in olla
seritur."--Linnaeus, 'Prolepsis,' Sec. iii.
[158] 'Rev. Hortic.' May, 1868, 'Gardeners' Chronicle,' 1868, pp. 572,
737.
[159] Cited in 'Annals Nat. Hist.,' 1845, vol. xv, p. 177.
[160] 'Ann. Scienc. Nat.,' vol. xiv, 1860, p. 13.
[161] Naudin, 'Ann. Sc. Nat.,' 2nd ser., 1840, vol. xiv, p. 14, fig. 6,
pl. i (_Drosera_). St. Hilaire, 'Comptes Rendus,' ix, p. 437.
[162] Hance, 'Hook. Journ. Botany,' 1849, vol. i, p. 141, pl. v.
[163] Booth, 'Gard. Chron.,' Jan. 1st, 1853, p. 4.
[164] Lindley, 'Theory of Horticulture,' ed. 2, p. 273.
[165] 'Hook. Journ. of Botany,' 1852, iv, p. 206. See also the curious
_Begonia gemmipara_, 'Hook. fil. Illust. Himal. Plant.,' t. xiv.
[166] 'Phytanth.,' n. 36, _d._
[167] 'Ann. Scienc. Nat.,' 3rd series. 1853. vol. xix, p. 251, tab. 14.
[168] Carriere, 'Revue Horticole.' 1868, p. 184.
[169] 'Gard. Chron.,' 1858, p. 556.
[170] 1863, p. 556, &c.
[171] 'Ann. Nat. Hist.,' 1845, vol. xvi, p. 355.
[172] See also Lindley, 'Veg. Kingd.,' p. 109 et 116_a_, where the views
of Raspail, R. Brown, Mohl, Henslow, and others, are discussed.
[173] It has been observed that if a plant is supplied with copious
nourishment the flowering-period is delayed; but that moderate or even
scanty nourishment accelerates it. Goethe, 'Metam.,' Sec. 30. See also
Wolff, 'Theoria Generationis,' 1759; Linn. 'Prolepsis,' Secs. 3 and 10.
[174] Moquin-Tandon, p. 384; also Lindl., 'Elements of Botany,' p. 65,
fig. 130; "Theory of Horticulture," p. 86. 'Gard. Chron.,' 1851, p. 723;
Irmish, 'Flora,' 1858, p. 38, &c.
[175] Caspary, 'Bull. Soc. Bot. Fr.,' vol. vi, 1859, p. 235; also Payer,
ibid., vol. i, 1854. p. 283.
[176] Trecul, 'Ann. Sc. Nat.,' 2nd ser., vol. xx, p. 339.
[177] 'Bull. Soc. Bot. Fr.,' vol. vii, 1858, p. 331.
[178] 'Bull. Soc. Bot. Fr.,' vol. i. p. 306, vol. v, p. 115. 'Illustr.
Hortic.,' xii, 1865, Misc. 79. 'Rev. Horticole,' 1860 p. 204, et 1867 p.
43.
[179] 'Bull. Soc. Bot. Fr.,' 1858, p. 685.
[180] The structure of this flower is discussed at some length in a
paper by the author on axillary prolification. 'Trans. Linn. Soc.,' vol.
xxiii, p. 486, t. liv. fig. 3. See also 'Clos. Bull. Soc. Bot. Fr.,'
vol. v, 1855, p. 672. Seringe et Heyland, 'Bull. Bot.,' i, p. 8. 'Pallas
Enum. Plant. Hort. Demidoff,' append, c, ic.
[181] 'Adansonia,' i, 181.
[182] 'Adansonia.' vol. iii, p. 351, tab. xii.
[183] 'Elem. Terat. Veget.,' p, 218.
[184] Masters, 'Journ. Linn. Soc.,' vol. ix, 1866, p. 334.
[185] 'Trans. Linn. Soc.,' vol. xxiv, p. 143. tab. xxiv.
[186] 'Brit. Assoc. Report,' Dundee, 1867; and Seemann's 'Journal of
Botany,' 1867, p. 319, tab. lxxii, figs. B 1-9.
[187] Duval Jouve, 'Hist. Equiset. France.' 1864, p. 154.
[188] 'Flora,' t. xxiv, 1841, p. 340.
[189] Moore, 'Nature-Printed British Ferns,' 8vo edition, vol. ii. p.
135. tab. lxxxv, B, &c.