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 above full size and in its natural position, 

 for a Utricularia (cf. 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-larvae 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 lacunae 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 laminae, which are 

 extremely like those of Dioncea in shape, and serve, as do the latter, for the capture 

 of small animals. Each leaf is differentiated, as in Dioncea, 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 4 ). 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 



