UTRICULARIA.
Utricularia neglecta—Structure of the bladder—The uses of the several
parts—Number of imprisoned animals—Manner of capture—The bladders
cannot digest animal matter, but absorb the products of its
decay—Experiments on the absorption of certain fluids by the quadrifid
processes—Absorption by the glands—Summary of the observation on
absorption— Development of the bladders—Utricularia
vulgaris—Utricularia minor—Utricularia clandestina.
I was led to investigate the habits and structure of the species of
this genus partly from their belonging to the same natural family as
Pinguicula, but more especially by Mr. Holland’s statement, that “water
insects are often found imprisoned in the bladders,” which he suspects
“are destined for the plant to feed on.”* The plants which I first
received as Utricularia vulgaris from the New Forest in Hampshire and
from Cornwall, and which I have chiefly worked on, have been determined
by Dr. Hooker to be a very rare British species, the Utricularia
neglecta of Lehm.** I subsequently received the true Utricularia
vulgaris from Yorkshire. Since drawing up the following description
from my own observations and those of my son, Francis Darwin, an
important memoir by Prof. Cohn
* The ‘Quart. Mag. of the High Wycombe Nat. Hist. Soc.’ July 1868, p.
5. Delpino (‘Ult. Osservaz. sulla Dicogamia,’ &c. 1868-1869, p. 16)
also quotes Crouan as having found (1858) crustaceans within the
bladders of Utricularia vulgaris.
** I am much indebted to the Rev. H.M. Wilkinson, of Bistern, for
having sent me several fine lots of this species from the New Forest.
Mr. Ralfs was also so kind as to send me living plants of the same
species from near Penzance in Cornwall. [page 396]
on Utricularia vulgaris has appeared;* and it has been no small
satisfaction to me to find that my account agrees almost completely
with that of this distinguished observer. I will publish my description
as it stood before reading that by Prof. Cohn, adding occasionally some
statements on his authority.
FIG. 17. (Utricularia neglecta.) Branch with the divided leaves bearing
bladders; about twice enlarged.
Utricularia neglecta.—The general appearance of a branch (about twice
enlarged), with the pinnatifid leaves bearing bladders, is represented
in the above sketch (fig. 17). The leaves continually bifurcate, so
that a full-grown one terminates in from twenty to thirty
* ‘Beitrage zur Biologie der Plflanzen’ drittes Heft, 1875. [page 397]
points. Each point is tipped by a short, straight bristle; and slight
notches on the sides of the leaves bear similar bristles. On both
surfaces there are many small papillae, crowned with two hemispherical
cells in close contact. The plants float near the surface of the water,
and are quite destitute of roots, even during the earliest period of
growth.* They commonly inhabit, as more than one observer has remarked
to me, remarkably foul ditches.
The bladders offer the chief point of interest. There are often two or
three on the same divided leaf, generally near the base; though I have
seen a single one growing from the stem. They are supported on short
footstalks. When fully grown, they are nearly 1/10 of an inch (2.54
mm.) in length. They are translucent, of a green colour, and the walls
are formed of two layers of cells. The exterior cells are polygonal and
rather large; but at many of the points where the angles meet, there
are smaller rounded cells. These latter support short conical
projections, surmounted by two hemispherical cells in such close
apposition that they appear united; but they often separate a little
when immersed in certain fluids. The papillae thus formed are exactly
like those on the surfaces of the leaves. Those on the same bladder
vary much in size; and there are a few, especially on very young
bladders, which have an elliptical instead of a circular outline. The
two terminal cells are transparent, but must hold much matter in
solution, judging from the quantity coagulated by prolonged immersion
in alcohol or ether.
* I infer that this is the case from a drawing of a seedling given by
Dr. Warming in his paper, “Bidrag til Kundskaben om Lentibulariaceae,”
from the ‘Videnskabelige Meddelelser,’ Copenhagen, 1874, Nos. 3-7, pp.
33-58.) [page 398]
The bladders are filled with water. They generally, but by no means
always, contain bubbles of air. According to the quantity of the
contained water and air, they vary much in thickness, but are always
somewhat compressed. At an early stage of growth, the flat or ventral
surface faces the axis or stem; but the footstalks must have some power
of movement; for in plants kept in my greenhouse the ventral surface
was generally turned either straight or obliquely downwards. The Rev.
H.M. Wilkinson examined
FIG. 18. (Utricularia neglecta.) Bladder; much enlarged. c, collar
indistinctly seen through the walls.
plants for me in a state of nature, and found this commonly to be the
case, but the younger bladders often had their valves turned upwards.
The general appearance of a bladder viewed laterally, with the
appendages on the near side alone represented, is shown in the
accompanying figure (fig. 18). The lower side, where the footstalk
arises, is nearly straight, and I have called it the ventral surface.
The other or dorsal surface is convex, and terminates in two long
prolongations, formed of several rows of cells, containing chlorophyll,
and bearing, chiefly on [page 399] the outside, six or seven long,
pointed, multicellular bristles. These prolongations of the bladder may
be conveniently called the antennæ, for the whole bladder (see fig. 17)
curiously resembles an entomostracan crustacean, the short footstalk
representing the tail. In fig. 18, the near antenna alone is shown.
Beneath the two antennæ the end of the bladder is slightly truncated,
and here is situated the most important part of the whole structure,
namely the entrance and valve. On each side of the entrance from three
to rarely seven long, multicellular bristles project out-
FIG. 19. (Utricularia neglecta.) Valve of bladder; greatly enlarged.
wards; but only those (four in number) on the near side are shown in
the drawing. These bristles, together with those borne by the antennæ,
form a sort of hollow cone surrounding the entrance.
The valve slopes into the cavity of the bladder, or upwards in fig. 18.
It is attached on all sides to the bladder, excepting by its posterior
margin, or the lower one in fig. 19, which is free, and forms one side
of the slit-like orifice leading into the bladder. This margin is
sharp, thin, and smooth, and rests on the edge of a rim or collar,
which dips deeply into the [page 400] bladder, as shown in the
longitudinal section (fig. 20) of the collar and valve; it is also
shown at c, in fig. 18. The edge of the valve can thus open only
inwards. As both the valve and collar dip into the bladder, a hollow or
depression is here formed, at the base of which lies the slit-like
orifice.
The valve is colourless, highly transparent, flexible and elastic. It
is convex in a transverse direction, but has been drawn (fig. 19) in a
flattened state, by which its apparent breadth is increased. It is
formed,
FIG. 20. (Utricularia neglecta.) Longitudinal vertical section through
the ventral portion of a bladder; showing valve and collar. v, valve;
the whole projection above c forms the collar; b, bifid processes; s,
ventral surface of bladder.
according to Cohn, of two layers of small cells, which are continuous
with the two layers of larger cells forming the walls of the bladder,
of which it is evidently a prolongation. Two pairs of transparent
pointed bristles, about as long as the valve itself, arise from near
the free posterior margin (fig. 18), and point obliquely outwards in
the direction of the antennæ. There are also on the surface of the
valve numerous glands, as I will call them; for they have the power of
absorption, though I doubt whether they ever secrete. They consist of
three kinds, which [page 401] to a certain extent graduate into one
another. Those situated round the anterior margin of the valve (upper
margin in fig. 19) are very numerous and crowded together; they consist
of an oblong head on a long pedicel. The pedicel itself is formed of an
elongated cell, surmounted by a short one. The glands towards the free
posterior margin are much larger, few in number, and almost spherical,
having short footstalks; the head is formed by the confluence of two
cells, the lower one answering to the short upper cell of the pedicel
of the oblong glands. The glands of the third kind have transversely
elongated heads, and are seated on very short footstalks; so that they
stand parallel and close to the surface of the valve; they may be
called the two-armed glands. The cells forming all these glands contain
a nucleus, and are lined by a thin layer of more or less granular
protoplasm, the primordial utricle of Mohl. They are filled with fluid,
which must hold much matter in solution, judging from the quantity
coagulated after they have been long immersed in alcohol or ether. The
depression in which the valve lies is also lined with innumerable
glands; those at the sides having oblong heads and elongated pedicels,
exactly like the glands on the adjoining parts of the valve.
The collar (called the peristome by Cohn) is evidently formed, like the
valve, by an inward projection of the walls of the bladder. The cells
composing the outer surface, or that facing the valve, have rather
thick walls, are of a brownish colour, minute, very numerous, and
elongated; the lower ones being divided into two by vertical
partitions. The whole presents a complex and elegant appearance. The
cells forming the inner surface are continuous with those over the
whole inner surface of the bladder. The space be- [page 402] tween the
inner and outer surface consists of coarse cellular tissue (fig. 20).
The inner side is thickly covered with delicate bifid processes,
hereafter to be described. The collar is thus made thick; and it is
rigid, so that it retains the same outline whether the bladder contains
little or much air and water. This is of great importance, as otherwise
the thin and flexible valve would be liable to be distorted, and in
this case would not act properly.
Altogether the entrance into the bladder, formed by the transparent
valve, with its four obliquely projecting bristles, its numerous
diversely shaped glands, surrounded by the collar, bearing glands on
the inside and bristles on the outside, together with the bristles
borne by the antennæ, presents an extraordinarily complex appearance
when viewed under the microscope.
We will now consider the internal structure of the bladder. The whole
inner surface, with the exception of the valve, is seen under a
moderately high power to be covered with a serried mass of processes
(fig. 21). Each of these consists of four divergent arms; whence their
name of quadrifid processes. They arise from small angular cells, at
the junctions of the angles of the larger cells which form the interior
of the bladder. The middle part of the upper surface of these small
cells projects a little, and then contracts into a very short and
narrow footstalk which bears the four arms (fig. 22.). Of these, two
are long, but often of not quite equal length, and project obliquely
inwards and towards the posterior end of the bladder. The two others
are much shorter, and project at a smaller angle, that is, are more
nearly horizontal, and are directed towards the anterior end of the
bladder. These arms are only moderately sharp; they are composed of ex-
[page 403] tremely thin transparent membrane, so that they can be bent
or doubled in any direction without being broken. They are lined with a
delicate layer of protoplasm, as is likewise the short conical
projection from which they arise. Each arm generally (but not
invariably) contains a minute, faintly brown particle, either rounded
or more commonly elongated, which exhibits incessant Brownian
movements. These par-
FIG. 21. (Utricularia neglecta.) Small portion of inside of bladder,
much enlarged, showing quadrifid processes.
FIG. 22. (Utricularia neglecta.) One of the quadrifid processes greatly
enlarged.
ticles slowly change their positions, and travel from one end to the
other of the arms, but are commonly found near their bases. They are
present in the quadrifids of young bladders, when only about a third of
their full size. They do not resemble ordinary nuclei, but I believe
that they are nuclei in a modified condition, for when absent, I could
occasionally just distinguish in their places a delicate halo of
matter, including a darker spot. Moreover, the quadrifids of
Utricularia montana contain rather larger and much [page 404] more
regularly spherical, but otherwise similar, particles, which closely
resemble the nuclei in the cells forming the walls of the bladders. In
the present case there were sometimes two, three, or even more, nearly
similar particles within a single arm; but, as we shall hereafter see,
the presence of more than one seemed always to be connected with the
absorption of decayed matter.
The inner side of the collar (see the previous fig. 20) is covered with
several crowded rows of processes, differing in no important respect
from the quadrifids, except in bearing only two arms instead of four;
they are, however, rather narrower and more delicate. I shall call them
the bifids. They project into the bladder, and are directed towards its
posterior end. The quadrifid and bifid processes no doubt are
homologous with the papillae on the outside of the bladder and of the
leaves; and we shall see that they are developed from closely similar
papillae.
The Uses of the several Parts.—After the above long but necessary
description of the parts, we will turn to their uses. The bladders have
been supposed by some authors to serve as floats; but branches which
bore no bladders, and others from which they had been removed, floated
perfectly, owing to the air in the intercellular spaces. Bladders
containing dead and captured animals usually include bubbles of air,
but these cannot have been generated solely by the process of decay, as
I have often seen air in young, clean, and empty bladders; and some old
bladders with much decaying matter had no bubbles.
The real use of the bladders is to capture small aquatic animals, and
this they do on a large scale. In the first lot of plants, which I
received from the New Forest early in July, a large proportion of the
fully [page 405] grown bladders contained prey; in a second lot,
received in the beginning of August, most of the bladders were empty,
but plants had been selected which had grown in unusually pure water.
In the first lot, my son examined seventeen bladders, including prey of
some kind, and eight of these contained entomostracan crustaceans,
three larvæ of insects, one being still alive, and six remnants of
animals so much decayed that their nature could not be distinguished. I
picked out five bladders which seemed very full, and found in them
four, five, eight, and ten crustaceans, and in the fifth a single much
elongated larva. In five other bladders, selected from containing
remains, but not appearing very full, there were one, two, four, two,
and five crustaceans. A plant of Utricularia vulgaris, which had been
kept in almost pure water, was placed by Cohn one evening into water
swarming with crustaceans, and by the next morning most of the bladders
contained these animals entrapped and swimming round and round their
prisons. They remained alive for several days; but at last perished,
asphyxiated, as I suppose, by the oxygen in the water having been all
consumed. Freshwater worms were also found by Cohn in some bladders. In
all cases the bladders with decayed remains swarmed with living Algae
of many kinds, Infusoria, and other low organisms, which evidently
lived as intruders.
Animals enter the bladders by bending inwards the posterior free edge
of the valve, which from being highly elastic shuts again instantly. As
the edge is extremely thin, and fits closely against the edge of the
collar, both projecting into the bladder (see section, fig. 20), it
would evidently be very difficult for any animal to get out when once
imprisoned, and apparently they never do escape. To show how closely
the edge [page 406] fits, I may mention that my son found a Daphnia
which had inserted one of its antennæ into the slit, and it was thus
held fast during a whole day. On three or four occasions I have seen
long narrow larvæ, both dead and alive, wedged between the corner of
the valve and collar, with half their bodies within the bladder and
half out.
As I felt much difficulty in understanding how such minute and weak
animals, as are often captured, could force their way into the
bladders, I tried many experiments to ascertain how this was effected.
The free margin of the valve bends so easily that no resistance is felt
when a needle or thin bristle is inserted. A thin human hair, fixed to
a handle, and cut off so as to project barely 1/4 of an inch, entered
with some difficulty; a longer piece yielded instead of entering. On
three occasions minute particles of blue glass (so as to be easily
distinguished) were placed on valves whilst under water; and on trying
gently to move them with a needle, they disappeared so suddenly that,
not seeing what had happened, I thought that I had flirted them off;
but on examining the bladders, they were found safely enclosed. The
same thing occurred to my son, who placed little cubes of green
box-wood (about 1/60 of an inch, .423 mm.) on some valves; and thrice
in the act of placing them on, or whilst gently moving them to another
spot, the valve suddenly opened and they were engulfed. He then placed
similar bits of wood on other valves, and moved them about for some
time, but they did not enter. Again, particles of blue glass were
placed by me on three valves, and extremely minute shavings of lead on
two other valves; after 1 or 2 hrs. none had entered, but in from 2 to
5 hrs. all five were enclosed. One of the particles of glass was a
[page 407] long splinter, of which one end rested obliquely on the
valve, and after a few hours it was found fixed, half within the
bladder and half projecting out, with the edge of the valve fitting
closely all round, except at one angle, where a small open space was
left. It was so firmly fixed, like the above-mentioned larvæ, that the
bladder was torn from the branch and shaken, and yet the splinter did
not fall out. My son also placed little cubes (about 1/65 of an inch,
.391 mm.) of green box-wood, which were just heavy enough to sink in
water, on three valves. These were examined after 19 hrs. 30 m., and
were still lying on the valves; but after 22 hrs. 30 m. one was found
enclosed. I may here mention that I found in a bladder on a naturally
growing plant a grain of sand, and in another bladder three grains;
these must have fallen by some accident on the valves, and then entered
like the particles of glass.
The slow bending of the valve from the weight of particles of glass and
even of box-wood, though largely supported by the water, is, I suppose,
analogous to the slow bending of colloid substances. For instance,
particles of glass were placed on various points of narrow strips of
moistened gelatine, and these yielded and became bent with extreme
slowness. It is much more difficult to understand how gently moving a
particle from one part of a valve to another causes it suddenly to
open. To ascertain whether the valves were endowed with irritability,
the surfaces of several were scratched with a needle or brushed with a
fine camel-hair brush, so as to imitate the crawling movement of small
crustaceans, but the valve did not open. Some bladders, before being
brushed, were left for a time in water at temperatures between 80° and
130° F. (26°.6-54°.4 Cent.), as, judging from a wide- [page 408] spread
analogy, this would have rendered them more sensitive to irritation, or
would by itself have excited movement; but no effect was produced. We
may, therefore, conclude that animals enter merely by forcing their way
through the slit-like orifice; their heads serving as a wedge. But I am
surprised that such small and weak creatures as are often captured (for
instance, the nauplius of a crustacean, and a tardigrade) should be
strong enough to act in this manner, seeing that it was difficult to
push in one end of a bit of a hair 1/4 of an inch in length.
Nevertheless, it is certain that weak and small creatures do enter, and
Mrs. Treat, of New Jersey, has been more successful than any other
observer, and has often witnessed in the case of Utricularia
clandestina the whole process.* She saw a tardigrade slowly walking
round a bladder, as if reconnoitring; at last it crawled into the
depression where the valve lies, and then easily entered. She also
witnessed the entrapment of various minute crustaceans. Cypris “was
quite wary, but nevertheless was often caught. Coming to the entrance
of a bladder, it would sometimes pause a moment, and then dash away; at
other times it would come close up, and even venture part of the way
into the entrance and back out as if afraid. Another, more heedless,
would open the door and walk in; but it was no sooner in than it
manifested alarm, drew in its feet and antennæ, and closed its shell.”
Larvæ, apparently of gnats, when “feeding near the entrance, are pretty
certain to run their heads into the net, whence there is no retreat. A
large larva is sometimes three or four hours in being swallowed, the
process bringing to
* ‘New York Tribune,’ reprinted in the ‘Gard. Chron.’ 1875, p. 303.
[page 409]
mind what I have witnessed when a small snake makes a large frog its
victim.” But as the valve does not appear to be in the least irritable,
the slow swallowing process must be the effect of the onward movement
of the larva.
It is difficult to conjecture what can attract so many creatures,
animal- and vegetable-feeding crustaceans, worms, tardigrades, and
various larvæ, to enter the bladders. Mrs. Treat says that the larvæ
just referred to are vegetable-feeders, and seem to have a special
liking for the long bristles round the valve, but this taste will not
account for the entrance of animal-feeding crustaceans. Perhaps small
aquatic animals habitually try to enter every small crevice, like that
between the valve and collar, in search of food or protection. It is
not probable that the remarkable transparency of the valve is an
accidental circumstance, and the spot of light thus formed may serve as
a guide. The long bristles round the entrance apparently serve for the
same purpose. I believe that this is the case, because the bladders of
some epiphytic and marsh species of Utricularia which live embedded
either in entangled vegetation or in mud, have no bristles round the
entrance, and these under such conditions would be of no service as a
guide. Nevertheless, with these epiphytic and marsh species, two pairs
of bristles project from the surface of the valve, as in the aquatic
species; and their use probably is to prevent too large animals from
trying to force an entrance into the bladder, thus rupturing orifice.
As under favourable circumstances most of the bladders succeed in
securing prey, in one case as many as ten crustaceans;—as the valve is
so well fitted to [page 410] allow animals to enter and to prevent
their escape;—and as the inside of the bladder presents so singular a
structure, clothed with innumerable quadrifid and bifid processes, it
is impossible to doubt that the plant has been specially adapted for
securing prey. From the analogy of Pinguicula, belonging to the same
family, I naturally expected that the bladders would have digested
their prey; but this is not the case, and there are no glands fitted
for secreting the proper fluid. Nevertheless, in order to test their
power of digestion, minute fragments of roast meat, three small cubes
of albumen, and three of cartilage, were pushed through the orifice
into the bladders of vigorous plants. They were left from one day to
three days and a half within, and the bladders were then cut open; but
none of the above substances exhibited the least signs of digestion or
dissolution; the angles of the cubes being as sharp as ever. These
observations were made subsequently to those on Drosera, Dionaea,
Drosophyllum, and Pinguicula; so that I was familiar with the
appearance of these substances when undergoing the early and final
stages of digestion. We may therefore conclude that Utricularia cannot
digest the animals which it habitually captures.
In most of the bladders the captured animals are so much decayed that
they form a pale brown, pulpy mass, with their chitinous coats so
tender that they fall to pieces with the greatest ease. The black
pigment of the eye-spots is preserved better than anything else. Limbs,
jaws, &c. are often found quite detached; and this I suppose is the
result of the vain struggles of the later captured animals. I have
sometimes felt surprised at the small proportion of imprisoned animals
in a fresh state compared with those utterly decayed. Mrs. Treat states
with respect [page 411] to the larvæ above referred to, that “usually
in less than two days after a large one was captured the fluid contents
of the bladders began to assume a cloudy or muddy appearance, and often
became so dense that the outline of the animal was lost to view.” This
statement raises the suspicion that the bladders secrete some ferment
hastening the process of decay. There is no inherent improbability in
this supposition, considering that meat soaked for ten minutes in water
mingled with the milky juice of the papaw becomes quite tender and soon
passes, as Browne remarks in his ‘Natural History of Jamaica,’ into a
state of putridity.
Whether or not the decay of the imprisoned animals is an any way
hastened, it is certain that matter is absorbed from them by the
quadrifid and bifid processes. The extremely delicate nature of the
membrane of which these processes are formed, and the large surface
which they expose, owing to their number crowded over the whole
interior of the bladder, are circumstances all favouring the process of
absorption. Many perfectly clean bladders which had never caught any
prey were opened, and nothing could be distinguished with a No. 8
object-glass of Hartnack within the delicate, structureless
protoplasmic lining of the arms, excepting in each a single yellowish
particle or modified nucleus. Sometimes two or even three such
particles were present; but in this case traces of decaying matter
could generally be detected. On the other hand, in bladders containing
either one large or several small decayed animals, the processes
presented a widely different appearance. Six such bladders were
carefully examined; one contained an elongated, coiled-up larva;
another a single large entomostracan crustacean, and the others from
two to five smaller ones, all [page 412] in a decayed state. In these
six bladders, a large number of the quadrifid processes contained
transparent, often yellowish, more or less confluent, spherical or
irregularly shaped, masses of matter. Some of the processes, however,
contained only fine granular matter, the particles of which were so
small that they could not be defined clearly with No. 8 of Hartnack.
The delicate layer of protoplasm lining their walls was in some cases a
little shrunk. On three occasions the above small masses of matter were
observed and sketched at short intervals of time; and they certainly
changed their positions relatively to each other and to the walls of
the arms. Separate masses sometimes became confluent, and then again
divided. A single little mass would send out a projection, which after
a time separated itself. Hence there could be no doubt that these
masses consisted of protoplasm. Bearing in mind that many clean
bladders were examined with equal care, and that these presented no
such appearance, we may confidently believe that the protoplasm in the
above cases had been generated by the absorption of nitrogenous matter
from the decaying animals. In two or three other bladders, which at
first appeared quite clean, on careful search a few processes were
found, with their outsides clogged with a little brown matter, showing
that some minute animal had been captured and had decayed, and the arms
here included a very few more or less spherical and aggregated masses;
the processes in other parts of the bladders being empty and
transparent. On the other hand, it must be stated that in three
bladders containing dead crustaceans, the processes were likewise
empty. This fact may be accounted for by the animals not having been
sufficiently decayed, or by time enough not having been allowed for the
generation of proto- [page 413] plasm, or by its subsequent absorption
and transference to other parts of the plant. It will hereafter be seen
that in three or four other species of Utricularia the quadrifid
processes in contact with decaying animals likewise contained
aggregated masses of protoplasm.
On the Absorption of certain Fluids by the Quadrifid and Bifid
processes.—These experiments were tried to ascertain whether certain
fluids, which seemed adapted for the purpose, would produce the same
effects on the processes as the absorption of decayed animal matter.
Such experiments are, however, troublesome; for it is not sufficient
merely to place a branch in the fluid, as the valve shuts so closely
that the fluid apparently does not enter soon, if at all. Even when
bristles were pushed into the orifices, they were in several cases
wrapped so closely round by the thin flexible edge of the valve that
the fluid was apparently excluded; so that the experiments tried in
this manner are doubtful and not worth giving. The best plan would have
been to puncture the bladders, but I did not think of this till too
late, excepting in a few cases. In all such trials, however, it cannot
be ascertained positively that the bladder, though translucent, does
not contain some minute animal in the last stage of decay. Therefore
most of my experiments were made by cutting bladders longitudinally
into two; the quadrifids were examined with No. 8 of Hartnack, then
irrigated, whilst under the covering glass, with a few drops of the
fluid under trial, kept in a damp chamber, and re-examined after stated
intervals of time with the same power as before.
[Four bladders were first tried as a control experiment, in the manner
just described, in a solution of one part of gum arabic to 218 of
water, and two bladders in a solution of one part of sugar to 437 of
water; and in neither case was any [page 414] change perceptible in the
quadrifids or bifids after 21 hrs. Four bladders were then treated in
the same manner with a solution of one part of nitrate of ammonia to
437 of water, and re-examined after 21 hrs. In two of these the
quadrifids now appeared full of very finely granular matter, and their
protoplasmic lining or primordial utricle was a little shrunk. In the
third bladder, the quadrifids included distinctly visible granules, and
the primordial utricle was a little shrunk after only 8 hrs. In the
fourth bladder the primordial utricle in most of the processes was here
and there thickened into little, irregular, yellowish specks; and from
the gradations which could be traced in this and other cases, these
specks appear to give rise to the larger free granules contained within
some of the processes. Other bladders, which, as far as could be
judged, had never caught any prey, were punctured and left in the same
solution for 17 hrs.; and their quadrifids now contained very fine
granular matter.
A bladder was bisected, examined, and irrigated with a solution of one
part of carbonate of ammonia to 437 of water. After 8 hrs. 30 m. the
quadrifids contained a good many granules, and the primordial utricle
was somewhat shrunk; after 23 hrs. the quadrifids and bifids contained
many spheres of hyaline matter, and in one arm twenty-four such spheres
of moderate size were counted. Two bisected bladders, which had been
previously left for 21 hrs. in the solution of gum (one part to 218 of
water) without being affected, were irrigated with the solution of
carbonate of ammonia; and both had their quadrifids modified in nearly
the same manner as just described,—one after only 9 hrs., and the other
after 24 hrs. Two bladders which appeared never to have caught any prey
were punctured and placed in the solution; the quadrifids of one were
examined after 17 hrs., and found slightly opaque; the quadrifids of
the other, examined after 45 hrs., had their primordial utricles more
or less shrunk with thickened yellowish specks, like those due to the
action of nitrate of ammonia. Several uninjured bladders were left in
the same solution, as well as a weaker solution of one part to 1750 of
water, or 1 gr. to 4 oz.; and after two days the quadrifids were more
or less opaque, with their contents finely granular; but whether the
solution had entered by the orifice, or had been absorbed from the
outside, I know not.
Two bisected bladders were irrigated with a solution of one part of
urea to 218 of water; but when this solution was employed, I forgot
that it had been kept for some days in a warm room, and had therefore
probably generated ammonia; anyhow [page 415] the quadrifids were
affected after 21 hrs. as if a solution of carbonate of ammonia had
been used; for the primordial utricle was thickened in specks, which
seemed to graduate into separate granules. Three bisected bladders were
also irrigated with a fresh solution of urea of the same strength;
their quadrifids after 21 hrs. were much less affected than in the
former case; nevertheless, the primordial utricle in some of the arms
was a little shrunk, and in others was divided into two almost
symmetrical sacks.
Three bisected bladders, after being examined, were irrigated with a
putrid and very offensive infusion of raw meat. After 23 hrs. the
quadrifids and bifids in all three specimens abounded with minute,
hyaline, spherical masses; and some of their primordial utricles were a
little shrunk. Three bisected bladders were also irrigated with a fresh
infusion of raw meat; and to my surprise the quadrifids in one of them
appeared, after 23 hrs., finely granular, with their primordial
utricles somewhat shrunk and marked with thickened yellowish specks; so
that they had been acted on in the same manner as by the putrid
infusion or by the salts of ammonia. In the second bladder some of the
quadrifids were similarly acted on, though to a very slight degree;
whilst the third bladder was not at all affected.]
From these experiments it is clear that the quadrifid and bifid
processes have the power of absorbing carbonate and nitrate of ammonia,
and matter of some kind from a putrid infusion of meat. Salts of
ammonia were selected for trial, as they are known to be rapidly
generated by the decay of animal matter in the presence of air and
water, and would therefore be generated within the bladders containing
captured prey. The effect produced on the processes by these salts and
by a putrid infusion of raw meat differs from that produced by the
decay of the naturally captured animals only in the aggregated masses
of protoplasm being in the latter case of larger size; but it is
probable that the fine granules and small hyaline spheres produced by
the solutions would coalesce into larger masses, with time enough
allowed. [page 416] We have seen with Drosera that the first effect of
a weak solution of carbonate of ammonia on the cell-contents is the
production of the finest granules, which afterwards aggregate into
larger, more or less rounded, masses; and that the granules in the
layer of protoplasm which flows round the walls ultimately coalesce
with these masses. Changes of this nature are, however, far more rapid
in Drosera than in Utricularia. Since the bladders have no power of
digesting albumen, cartilage, or roast meat, I was surprised that
matter was absorbed, at least in one case, from a fresh infusion of raw
meat. I was also surprised, from what we shall presently see with
respect to the glands round the orifice, that a fresh solution of urea
produced only a moderate effect on the quadrifids.
As the quadrifids are developed from papillae which at first closely
resemble those on the outside of the bladders and on the surfaces of
the leaves, I may here state that the two hemispherical cells with
which these latter papillae are crowned, and which in their natural
state are perfectly transparent, likewise absorb carbonate and nitrate
of ammonia; for, after an immersion of 23 hrs. in solutions of one part
of both these salts to 437 of water, their primordial utricles were a
little shrunk and of a pale brown tint, and sometimes finely granular.
The same result followed from the immersion of a whole branch for
nearly three days in a solution of one part of the carbonate to 1750 of
water. The grains of chlorophyll, also, in the cells of the leaves on
this branch became in many places aggregated into little green masses,
which were often connected together by the finest threads.
On the Absorption of certain Fluids by the Glands on the Valve and
Collar.—The glands round the orifices of bladders which are still
young, or which have been [page 417] long kept in moderately pure
water, are colourless; and their primordial utricles are only slightly
or hardly at all granular. But in the greater number of plants in a
state of nature—and we must remember that they generally grow in very
foul water—and with plants kept in an aquarium in foul water, most of
the glands were of a pale brownish tint; their primordial utricles were
more or less shrunk, sometimes ruptured, with their contents often
coarsely granular or aggregated into little masses. That this state of
the glands is due to their having absorbed matter from the surrounding
water, I cannot doubt; for, as we shall immediately see, nearly the
same results follow from their immersion for a few hours in various
solutions. Nor is it probable that this absorption is useless, seeing
that it is almost universal with plants growing in a state of nature,
excepting when the water is remarkably pure.
The pedicels of the glands which are situated close to the slit-like
orifice, both those on the valve and on the collar, are short; whereas
the pedicels of the more distant glands are much elongated and project
inwards. The glands are thus well placed so to be washed by any fluid
coming out of the bladder through the orifice. The valve fits so
closely, judging from the result of immersing uninjured bladders in
various solutions, that it is doubtful whether any putrid fluid
habitually passes outwards. But we must remember that a bladder
generally captures several animals; and that each time a fresh animal
enters, a puff of foul water must pass out and bathe the glands.
Moreover, I have repeatedly found that, by gently pressing bladders
which contained air, minute bubbles were driven out through the
orifice; and if a bladder is laid on blotting paper and gently pressed,
water oozes out. [page 418] In this latter case, as soon as the
pressure is relaxed, air is drawn in, and the bladder recovers its
proper form. If it is now placed under water and again gently pressed,
minute bubbles issue from the orifice and nowhere else, showing that
the walls of the bladder have not been ruptured. I mention this because
Cohn quotes a statement by Treviranus, that air cannot be forced out of
a bladder without rupturing it. We may therefore conclude that whenever
air is secreted within a bladder already full of water, some water will
be slowly driven out through the orifice. Hence I can hardly doubt that
the numerous glands crowded round the orifice are adapted to absorb
matter from the putrid water, which will occasionally escape from
bladders including decayed animals.
[In order to test this conclusion, I experimented with various
solutions on the glands. As in the case of the quadrifids, salts of
ammonia were tried, since these are generated by the final decay of
animal matter under water. Unfortunately the glands cannot be carefully
examined whilst attached to the bladders in their entire state. Their
summits, therefore, including the valve, collar, and antennæ, were
sliced off, and the condition of the glands observed; they were then
irrigated, whilst beneath a covering glass, with the solutions, and
after a time re-examined with the same power as before, namely No. 8 of
Hartnack. The following experiments were thus made.
As a control experiment solutions of one part of white sugar and of one
part of gum to 218 of water were first used, to see whether these
produced any change in the glands. It was also necessary to observe
whether the glands were affected by the summits of the bladders having
been cut off. The summits of four were thus tried; one being examined
after 2 hrs. 30 m., and the other three after 23 hrs.; but there was no
marked change in the glands of any of them.
Two summits bearing quite colourless glands were irrigated with a
solution of carbonate of ammonia of the same strength (viz. one part to
218 of water) , and in 5 m. the primordial utricles of most of the
glands were somewhat contracted; they were also thickened in specks or
patches, and had assumed a pale [page 419] brown tint. When looked at
again after 1 hr. 30 m., most of them presented a somewhat different
appearance. A third specimen was treated with a weaker solution of one
part of the carbonate to 437 of water, and after 1 hr. the glands were
pale brown and contained numerous granules.
Four summits were irrigated with a solution of one part of nitrate of
ammonia to 437 of water. One was examined after 15 m., and the glands
seemed affected; after 1 hr. 10 m. there was a greater change, and the
primordial utricles in most of them were somewhat shrunk, and included
many granules. In the second specimen, the primordial utricles were
considerably shrunk and brownish after 2 hrs. Similar effects were
observed in the two other specimens, but these were not examined until
21 hrs. had elapsed. The nuclei of many of the glands apparently had
increased in size. Five bladders on a branch, which had been kept for a
long time in moderately pure water, were cut off and examined, and
their glands found very little modified. The remainder of this branch
was placed in the solution of the nitrate, and after 21 hrs. two
bladders were examined, and all their glands were brownish, with their
primordial utricles somewhat shrunk and finely granular.
The summit of another bladder, the glands of which were in a
beautifully clear condition, was irrigated with a few drops of a mixed
solution of nitrate and phosphate of ammonia, each of one part to 437
of water. After 2 hrs. some few of the glands were brownish. After 8
hrs. almost all the oblong glands were brown and much more opaque than
they were before; their primordial utricles were somewhat shrunk and
contained a little aggregated granular matter. The spherical glands
were still white, but their utricles were broken up into three or four
small hyaline spheres, with an irregularly contracted mass in the
middle of the basal part. These smaller spheres changed their forms in
the course of a few hours and some of them disappeared. By the next
morning, after 23 hrs. 30 m., they had all disappeared, and the glands
were brown; their utricles now formed a globular shrunken mass in the
middle. The utricles of the oblong glands had shrunk very little, but
their contents were somewhat aggregated. Lastly, the summit of a
bladder which had been previously irrigated for 21 hrs. with a solution
of one part of sugar to 218 of water without being affected, was
treated with the above mixed solution; and after 8 hrs. 30 m. all the
glands became brown, with their primordial utricles slightly shrunk.
Four summits were irrigated with a putrid infusion of raw [page 420]
meat. No change in the glands was observable for some hours, but after
24 hrs. most of them had become brownish, and more opaque and granular
than they were before. In these specimens, as in those irrigated with
the salts of ammonia, the nuclei seemed to have increased both in size
and solidity, but they were not measured. Five summits were also
irrigated with a fresh infusion of raw meat; three of these were not at
all affected in 24 hrs., but the glands of the other two had perhaps
become more granular. One of the specimens which was not affected was
then irrigated with the mixed solution of the nitrate and phosphate of
ammonia, and after only 25 m. the glands contained from four or five to
a dozen granules. After six additional hours their primordial utricles
were greatly shrunk.
The summit of a bladder was examined, and all the glands found
colourless, with their primordial utricles not at all shrunk; yet many
of the oblong glands contained granules just resolvable with No. 8 of
Hartnack. It was then irrigated with a few drops of a solution of one
part of urea to 218 of water. After 2 hrs. 25 m. the spherical glands
were still colourless; whilst the oblong and two-armed ones were of a
brownish tint, and their primordial utricles much shrunk, some
containing distinctly visible granules. After 9 hrs. some of the
spherical glands were brownish, and the oblong glands were still more
changed, but they contained fewer separate granules; their nuclei, on
the other hand, appeared larger, as if they had absorbed the granules.
After 23 hrs. all the glands were brown, their primordial utricles
greatly shrunk, and in many cases ruptured.
A bladder was now experimented on, which was already somewhat affected
by the surrounding water; for the spherical glands, though colourless,
had their primordial utricles slightly shrunk; and the oblong glands
were brownish, with their utricles much, but irregularly, shrunk. The
summit was treated with the solution of urea, but was little affected
by it in 9 hrs.; nevertheless, after 23 hrs. the spherical glands were
brown, with their utricles more shrunk; several of the other glands
were still browner, with their utricles contracted into irregular
little masses.
Two other summits, with their glands colourless and their utricles not
shrunk, were treated with the same solution of urea. After 5 hrs. many
of the glands presented a shade of brown, with their utricles slightly
shrunk. After 20 hrs. 40 m. some few of them were quite brown, and
contained [page 421] irregularly aggregated masses; others were still
colourless, though their utricles were shrunk; but the greater number
were not much affected. This was a good instance of how unequally the
glands on the same bladder are sometimes affected, as likewise often
occurs with plants growing in foul water. Two other summits were
treated with a solution which had been kept during several days in a
warm room, and their glands were not at all affected when examined
after 21 hrs.
A weaker solution of one part of urea to 437 of water was next tried on
six summits, all carefully examined before being irrigated. The first
was re-examined after 8 hrs. 30 m., and the glands, including the
spherical ones, were brown; many of the oblong glands having their
primordial utricles much shrunk and including granules. The second
summit, before being irrigated, had been somewhat affected by the
surrounding water, for the spherical glands were not quite uniform in
appearance; and a few of the oblong ones were brown, with their
utricles shrunk. Of the oblong glands, those which were before
colourless, became brown in 3 hrs. 12 m. after irrigation, with their
utricles slightly shrunk. The spherical glands did not become brown,
but their contents seemed changed in appearance, and after 23 hrs.
still more changed and granular. Most of the oblong glands were now
dark brown, but their utricles were not greatly shrunk. The four other
specimens were examined after 3 hrs. 30 m., after 4 hrs., and 9 hrs.; a
brief account of their condition will be sufficient. The spherical
glands were not brown, but some of them were finely granular. Many of
the oblong glands were brown, and these, as well as others which still
remained colourless, had their utricles more or less shrunk, some of
them including small aggregated masses of matter.]
A Summary of the Observations on Absorption.—From the facts now given
there can be no doubt that the variously shaped glands on the valve and
round the collar have the power of absorbing matter from weak solutions
of certain salts of ammonia and urea, and from a putrid infusion of raw
meat. Prof. Cohn believes that they secrete slimy matter; but I was not
able to perceive any trace of such action, excepting that, after
immersion in alcohol, extremely fine lines could sometimes be seen
radiating from their [page 422] surfaces. The glands are variously
affected by absorption; they often become of a brown colour; sometimes
they contain very fine granules, or moderately sized grains, or
irregularly aggregated little masses; sometimes the nuclei appear to
have increased in size; the primordial utricles are generally more or
less shrunk and sometimes ruptured. Exactly the same changes may be
observed in the glands of plants growing and flourishing in foul water.
The spherical glands are generally affected rather differently from the
oblong and two-armed ones. The former do not so commonly become brown,
and are acted on more slowly. We may therefore infer that they differ
somewhat in their natural functions.
It is remarkable how unequally the glands on the bladders on the same
branch, and even the glands of the same kind on the same bladder, are
affected by the foul water in which the plants have grown, and by the
solutions which were employed. In the former case I presume that this
is due either to little currents bringing matter to some glands and not
to others, or to unknown differences in their constitution. When the
glands on the same bladder are differently affected by a solution, we
may suspect that some of them had previously absorbed a small amount of
matter from the water. However this may be, we have seen that the
glands on the same leaf of Drosera are sometimes very unequally
affected, more especially when exposed to certain vapours.
If glands which have already become brown, with their primordial
utricles shrunk, are irrigated with one of the effective solutions,
they are not acted on, or only slightly and slowly. If, however, a
gland contains merely a few coarse granules, this does not prevent a
solution from acting. I have never seen [page 423] any appearance
making it probable that glands which have been strongly affected by
absorbing matter of any kind are capable of recovering their pristine,
colourless, and homogeneous condition, and of regaining the power of
absorbing.
From the nature of the solutions which were tried, I presume that
nitrogen is absorbed by the glands; but the modified, brownish, more or
less shrunk, and aggregated contents of the oblong glands were never
seen by me or by my son to undergo those spontaneous changes of form
characteristic of protoplasm. On the other hand, the contents of the
larger spherical glands often separated into small hyaline globules or
irregularly shaped masses, which changed their forms very slowly and
ultimately coalesced, forming a central shrunken mass. Whatever may be
the nature of the contents of the several kinds of glands, after they
have been acted on by foul water or by one of the nitrogenous
solutions, it is probable that the matter thus generated is of service
to the plant, and is ultimately transferred to other parts.
The glands apparently absorb more quickly than do the quadrifid and
bifid processes; and on the view above maintained, namely that they
absorb matter from putrid water occasionally emitted from the bladders,
they ought to act more quickly than the processes; as these latter
remain in permanent contact with captured and decaying animals.
Finally, the conclusion to which we are led by the foregoing
experiments and observations is that the bladders have no power of
digesting animal matter, though it appears that the quadrifids are
somewhat affected by a fresh infusion of raw meat. It is certain that
the processes within the bladders, and the glands outside, absorb
matter from salts of [page 424] ammonia, from a putrid infusion of raw
meat, and from urea. The glands apparently are acted on more strongly
by a solution of urea, and less strongly by an infusion of raw meat,
than are the processes. The case of urea is particularly interesting,
because we have seen that it produces no effect on Drosera, the leaves
of which are adapted to digest fresh animal matter. But the most
important fact of all is, that in the present and following species the
quadrifid and bifid processes of bladders containing decayed animals
generally include little masses of spontaneously moving protoplasm;
whilst such masses are never seen in perfectly clean bladders.
Development of the Bladders.—My son and I spent much time over this
subject with small success. Our observations apply to the present
species and to Utricularia vulgaris, but were made chiefly on the
latter, as the bladders are twice as large as those of Utricularia
neglecta. In the early part of autumn the stems terminate in large
buds, which fall off and lie dormant during the winter at the bottom.
The young leaves forming these buds bear bladders in various stages of
early development. When the bladders of Utricularia vulgaris are about
1/100 inch (.254 mm.) in diameter (or 1/200 in the case of Utricularia
neglecta), they are circular in outline, with a narrow, almost closed,
transverse orifice, leading into a hollow filled with water; but the
bladders are hollow when much under 1/100 of an inch in diameter. The
orifices face inwards or towards the axis of the plant. At this early
age the bladders are flattened in the plane in which the orifice lies,
and therefore at right angles to that of the mature bladders. They are
covered exteriorly with papillae of different sizes, many of which have
an elliptical outline. A bundle of vessels, formed of [page 425] simple
elongated cells, runs up the short footstalk, and divides at the base
of the bladder. One branch extends up the middle of the dorsal surface,
and the other up the middle of the ventral surface. In full-grown
bladders the ventral bundle divides close beneath the collar, and the
two branches run on each side to near where the corners of the valve
unite with the collar; but these branches could not be seen in very
young bladders.
FIG. 23. (Utricularia vulgaris.) Longitudinal section through a young
bladder, 1/100 of an inch in length, with the orifice too widely open.
The accompanying figure (fig. 23) shows a section, which happened to be
strictly medial, through the footstalk and between the nascent antennæ
of a bladder of Utricularia vulgaris, 1/100 inch in diameter. The
specimen was soft, and the young valve became separated from the collar
to a greater degree than is natural, and is thus represented. We here
clearly see that the valve and collar are infolded prolongations of the
walls of the bladder. Even at this early age, glands could be detected
on the valve. The state of the quadrifid processes will presently be
described. The antennæ at this period consist of minute cellular
projections (not shown in the above figure, as they do not lie in the
medial plane), which soon bear incipient bristles. In five instances
the young antennæ were not of quite equal length; and this fact is
intelligible if I am right in believing that they represent two
divisions of the leaf, rising from the end of the bladder; for, with
the true leaves, whilst very young, the divisions are never, as far as
I have seen, strictly opposite; they [page 426] must therefore be
developed one after the other, and so it would be with the two antennæ.
At a much earlier age, when the half formed bladders are only 1/300
inch (.0846 mm.) in diameter or a little more, they present a totally
different appearance. One is represented on the left side of the
accompanying drawing (fig. 24). The young leaves
FIG. 24. (Utricularia vulgaris.) Young leaf from a winter bud, showing
on the left side a bladder in its earliest stage of development.
at this age have broad flattened segments, with their future divisions
represented by prominences, one of which is shown on the right side.
Now, in a large number of specimens examined by my son, the young
bladders appeared as if formed by the oblique folding over of the apex
and of one margin with a prominence, against the opposite margin. The
circular hollow between the infolded apex and infolded prominence
apparently contracts into the narrow orifice, wherein the valve and
collar will be developed; the bladder itself being formed by the
confluence of the opposed [page 427] margins of the rest of the leaf.
But strong objections may be urged against this view, for we must in
this case suppose that the valve and collar are developed
asymmetrically from the sides of the apex and prominence. Moreover, the
bundles of vascular tissue have to be formed in lines quite
irrespective of the original form of the leaf. Until gradations can be
shown to exist between this the earliest state and a young yet perfect
bladder, the case must be left doubtful.
As the quadrifid and bifid processes offer one of the greatest
peculiarities in the genus, I carefully observed their development in
Utricularia neglecta. In bladders about 1/100 of an inch in diameter,
the inner surface is studded with papillae, rising from small cells at
the junctions of the larger ones. These papillae consist of a delicate
conical protuberance, which narrows into a very short footstalk,
surmounted by two minute cells. They thus occupy the same relative
position, and closely resemble, except in being smaller and rather more
prominent, the papillae on the outside of the bladders, and on the
surfaces of the leaves. The two terminal cells of the papillae first
become much elongated in a line parallel to the inner surface of the
bladder. Next, each is divided by a longitudinal partition. Soon the
two half-cells thus formed separate from one another; and we now have
four cells or an incipient quadrifid process. As there is not space for
the two new cells to increase in breadth in their original plane, the
one slides partly under the other. Their manner of growth now changes,
and their outer sides, instead of their apices, continue to grow. The
two lower cells, which have slid partly beneath the two upper ones,
form the longer and more upright pair of processes; whilst the two
upper cells form the shorter [page 428] and more horizontal pair; the
four together forming a perfect quadrifid. A trace of the primary
division between the two cells on the summits of the papillae can still
be seen between the bases of the longer processes. The development of
the quadrifids is very liable to be arrested. I have seen a bladder
1/50 of an inch in length including only primordial papillae; and
another bladder, about half its full size, with the quadrifids in an
early stage of development.
As far as I could make out, the bifid processes are developed in the
same manner as the quadrifids, excepting that the two primary terminal
cells never become divided, and only increase in length. The glands on
the valve and collar appear at so early an age that I could not trace
their development; but we may reasonably suspect that they are
developed from papillae like those on the outside of the bladder, but
with their terminal cells not divided into two. The two segments
forming the pedicels of the glands probably answer to the conical
protuberance and short footstalk of the quadrifid and bifid processes.
I am strengthened in the belief that the glands are developed from
papillae like those on the outside of the bladders, from the fact that
in Utricularia amethystina the glands extend along the whole ventral
surface of the bladder close to the footstalk.
UTRICULARIA VULGARIS.
Living plants from Yorkshire were sent me by Dr. Hooker. This species
differs from the last in the stems and leaves being thicker or coarser;
their divisions form a more acute angle with one another; the notches
on the leaves bear three or four short bristles instead of one; and the
bladders are twice as large, or about 1/5 of an inch (5.08 mm.) in
diameter. In all essential respects the bladders resemble those of
Utricularia neglecta, but the sides of the peristome are perhaps a
little more [page 429] prominent, and always bear, as far as I have
seen, seven or eight long multicellular bristles. There are eleven long
bristles on each antenna, the terminal pair being included. Five
bladders, containing prey of some kind, were examined. The first
included five Cypris; a large copepod and a Diaptomus; the second, four
Cypris; the third, a single rather large crustacean; the fourth, six
crustaceans; and the fifth, ten. My son examined the quadrifid
processes in a bladder containing the remains of two crustaceans, and
found some of them full of spherical or irregularly shaped masses of
matter, which were observed to move and to coalesce. These masses
therefore consisted of protoplasm.
UTRICULARIA MINOR.
FIG. 25. (Utricularia minor.) Quadrifid process, greatly enlarged.
This rare species was sent me in a living state from Cheshire, through
the kindness of Mr. John Price. The leaves and bladders are much
smaller than those of Utricularia neglecta. The leaves bear fewer and
shorter bristles, and the bladders are more globular. The antennæ,
instead of projecting in front of the bladders, are curled under the
valve, and are armed with twelve or fourteen extremely long
multicellular bristles, generally arranged in pairs. These, with seven
or eight long bristles on both sides of the peristome, form a sort of
net over the valve, which would tend to prevent all animals, excepting
very small ones, entering the bladder. The valve and collar have the
same essential structure as in the two previous species; but the glands
are not quite so numerous; the oblong ones are rather more elongated,
whilst the two-armed ones are rather less elongated. The four bristles
which project obliquely from the lower edge of the valve are short.
Their shortness, compared with those on the valves of the foregoing
species, is intelligible if my view is correct that they serve to
prevent too large animals forcing an entrance through the valve, thus
injuring it; for the valve is already protected to a certain extent by
the incurved antennæ, together with the lateral bristles. The bifid
processes are like those in the previous species; but the quadrifids
differ in the four arms (fig. 25) [page 430] being directed to the same
side; the two longer ones being central, and the two shorter ones on
the outside.
The plants were collected in the middle of July; and the contents of
five bladders, which from their opacity seemed full of prey, were
examined. The first contained no less than twenty-four minute
fresh-water crustaceans, most of them consisting of empty shells, or
including only a few drops of red oily matter; the second contained
twenty; the third, fifteen; the fourth, ten, some of them being rather
larger than usual; and the fifth, which seemed stuffed quite full,
contained only seven, but five of these were of unusually large size.
The prey, therefore, judging from these five bladders, consists
exclusively of fresh-water crustaceans, most of which appeared to be
distinct species from those found in the bladders of the two former
species. In one bladder the quadrifids in contact with a decaying mass
contained numerous spheres of granular matter, which slowly changed
their forms and positions.
UTRICULARIA CLANDESTINA.
This North American species, which is aquatic like the three foregoing
ones, has been described by Mrs. Treat, of New Jersey, whose excellent
observations have already been largely quoted. I have not as yet seen
any full description by her of the structure of the bladder, but it
appears to be lined with quadrifid processes. A vast number of captured
animals were found within the bladders; some being crustaceans, but the
greater number delicate, elongated larvæ, I suppose of Culicidae. On
some stems, “fully nine out of every ten bladders contained these larvæ
or their remains.” The larvæ “showed signs of life from twenty-four to
thirty-six hours after being imprisoned,” and then perished. [page 431]