Ouap. XV. ON THE DROBERACES. 363 
growing in very poor soil, it would tend to be perfected 
through natural selection. Therefore, any ordinary 
plant having viscid glands, which occasionally caught 
insects, might thus be converted under favourable cir- 
cumstances 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 acquire- 
ment of the third remarkable character possessed by 
the more highly developed genera of the Droseracee, 
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, indepen- 
dently 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 
