152 PLANTS WHICH EXHIBIT MOVEMENTS IN THE CAPTURE OF PREY. 
to be the seat of origin of this phenomenon. A great alteration in the intensity of 
the current ensues upon each excitation of the leaf; and, inasmuch as this fluctuation 
of the electric current precedes the movement of the leaf caused by the stimulus, 
it is natural to assume that it depends upon the conduction and liberation of the 
stimulus. 
Aldrovandia, the plant nearest allied to the Fly-trap in the structure of its leaf, 
is a water-plant, which occurs scattered over the southern and central parts of 
Europe. It only flourishes in shallow ditches, pools, and small ponds inclosed by 
banks of reeds and rushes, where the plants are immersed in clear, so-called soft 
water, attaining in summer to a temperature of 30° C., and are exempt from any 
incrustation of carbonate of lime, whereby the tender parts of the leaves might 
be hindered in their movements. On cursory inspection, one might take Aldro- 
vandia vesiculosa, which is represented in fig. 29 full size and in its natural position, 
for a Utricularia (ef. fig. 17). It lives, like the latter, floating in water; is destitute 
of roots, and has a slender filiform stem with leaves arranged in whorls and ter- 
minating in bristles. In proportion as it grows at the apex, the hinder part dies 
away and decays. The development of hibernating buds takes place also in 
precisely the same manner as in Utricularia. Towards autumn, the stem ceases 
to elongate, and the two hundred small and young leaves, which adorn the ex- 
tremity of the stem and whose cells are quite full of starch, remain lying closely 
wrapped one upon another and form a dark, oval, bristly ball, which sinks at the 
commencement of winter to the bottom of the pool or pond and hibernates there 
lying upon the mud. 
It is not till very late in the following spring, when little midge-larve and 
other animals begin to move about in the water, that fresh life is awakened in 
these structures. The starch-grains in the leaves are brought into solution and 
used for building-material; the axis elongates, and lacun® filled with air are 
developed, whereupon the plant becomes lighter, ascends, and remains throughout 
the summer and autumn floating just below the surface of the water. Although 
the little leaves of the winter-buds generally admit of the recognition of their 
future form, the apparatus adapted to the capture of animals is but little developed 
on them. But when once the leaves are mature, they bear laminw, which are 
extremely like those of Dionea in shape, and serve, as do the latter, for the capture 
of small animals. Each leaf is differentiated, as in Dionea, into a strong, dark-green 
petiole expanded and anteriorly clavate, and into a roundish lamina with a delicate 
epidermis and with two lobes connected by the midrib and inclined nearly at right 
angles to one another (see fig. 28*). The midrib projects beyond the apex of the 
delicate lamina in the form of a bristle. In addition, comparatively long, rigid 
bristles, tipped with extremely fine spines, proceed from the petiole close to where 
the latter is joined to the lamina; and these bristles, which are directed forwards, 
give the whole leaf-structure a spiky appearance and prevent the approach of such 
animals as are not suitable for prey. The two margins of the lamina are bent 
inwards, and their rims are studded with small conical points. On the surface of 
