Cuar, XV} ON THE DROSERACEZ. 293 
be of high service to plants growing in very poor soil, it 
would tend to be perfected through natural selection. There- 
fore, any ordinary plant having viscid glands, which 
occasionally caught insects, might thus be converted under 
favourable circumstances into a species capable of true 
digestion. It ceases, therefore, to be any great mystery how 
several genera of plants, in no way closely related together, 
have independently acquired this same power. 
As there exist several plants the glands of which cannot, 
as far as is known, digest animal matter, yet can absorb salts 
of ammonia and animal fluids, it is probable that this latter 
power forms the first stage towards that of digestion. It 
might, however, happen, under certain conditions, that a 
plant, after having acquired the power of digestion, should 
degenerate into one capable only of absorbing animal matter 
in solution, or in a state of decay, or the final products of 
decay, namely the salts of ammonia. It would appear that 
this has actually occurred to a partial extent with the leaves 
of Aldrovanda; the outer parts of which possess absorbent 
organs, but no glands fitted for the secretion of any digestive 
fluid, these being confined to the inner parts. 
Little light can be thrown on the gradual acquirement of 
the third remarkable character possessed by the more highly 
developed genera of the Droseracew, namely the power of 
movement when excited. It should, however, be borne in 
mind that leaves and their homologues as well as flower- 
peduncles, have gained this power, in innumerable instances, 
independently of inheritance from any common parent form ; 
for instance, in tendril-bearers and leaf-climbers (i.e. plants 
with their leaves, petioles and flower-peduncles, &c., modified 
for prehension) belonging to a large number of the most 
widely distinct orders,—in the leaves of the many plants 
which go to sleep at night, or move when shaken, —and in 
irritable stamens and pistils of not a few species. We may 
therefore infer that the power of movement can be by some 
means readily acquired. Such movements imply irritability 
or sensitiveness, but, as Cohn has remarked,* the tissues of 
_ the plants thus endowed do not differ in any uniform manner 
* See the abstract of his memoir on the contractile tissues of plants, in the 
‘Annals and Mag. of Nat, Hist.’ 3rd series, vol. xi. p. 183. 
