356 CONCLUDING REMARKS Cuar. XV 
movement makes up for the loss of viscid secretion. 
In every case it is some part of the leaf which moves. 
In Aldrovanda it appears to be the basal parts alone 
which contract and carry with them the broad, thin 
margins of the lobes. In Dionza the whole lobe, with 
the exception of the marginal prolongations or spikes, 
curves inwards, though the chief seat of movement is 
near the midrib. In Drosera the chief seat is in the 
lower part of the tentacles, which, homologically, may 
be considered as prolongations of the leaf; but the 
whole blade often curls inwards, converting the leaf 
into a temporary stomach. 
There can hardly be a doubt that all the plants 
belonging to these six genera have the power of dis- 
solving animal matter by the aid of their secretion, 
which contains an acid, together with a ferment 
almost identical in nature with pepsin; and that they 
afterwards absorb the matter thus digested. ‘his is 
certainly the case with Drosera, Drosophyllum, and 
Dionea; almost certainly with Aldrovanda; and, from 
analogy, very probable with Roridula and Byblis. We 
can thus understand how it is that the three first- 
named genera are provided with such small roots, and 
that Aldrovanda is quite rootless; about the roots 
of the two other genera nothing is known. It is, no 
doubt, a surprising fact that a whole group of plants 
(and, as we shall presently see, some other plants 
not allied to the Droseracez) should subsist partly by 
digesting animal matter, and partly by decomposing 
carbonic acid, instead of exclusively by this latter 
means, together with the absorption of matter from 
the soil by the aid of roots. We have, however, an 
. equally anomalous case in the animal kingdom; the 
thizocephalous crustaceans do not feed like other 
animals by their mouths, for they are destitute of an 
