258 EVOLUTION OF PLANTS 
its upper surface. The peculiar digestive fluid which is 
present in both cases is probably a direct product of the 
plant itself, although it has been claimed that it is due 
to the presence of certain bacteria, which are present in 
large numbers. Whether the digestive process is due 
to the secretions of the plant itself, or to the activity 
of the bacteria, the products of digestion undoubtedly 
serve to supply the plant 
with nitrogenous food. 
The pitcher-plants, 
Nepenthes (Fig. 58, B), 
Sarracenia (Fig. 58, A), 
and Darlingtonia, are 
also striking examples of 
these carnivorous plants. 
All of these have the 
leaves modified into 
pitcher -shaped recepta- 
cles, into which insects 
are lured by the bright 
colors of the leaves as 
well as an abundant: se- 
cretion of a honey-like 
substance. In most of 
Fic. 58 (Carnivorous, plants).— A, 
leaf of the common pitcher-plant 
(Sarracenia purpurea) ; B, pitcher 
of a tropical pitcher-plant (Nepen- 
thes) borne upon the end of a ten- 
dril, the opening protected by a 
lid; C, leat of a sundew (Drosera 
longifolia); D, leaf of Drosera 
which has captured a mosquito, 
showing the way in which the ten- 
tacles, ten, clasp the insect ; E, part 
of a leaf of bladder-weed (Utricu- 
laria), with the bladder-like trap, 
v; F, a single vesicle of Utricu- 
laria more enlarged. (Figs. A, B 
after Goebel.) 
insect which has fallen in 
them the upper part of 
the interior of the pitcher 
is lined with stiff, down- 
ward pointing hairs, be- 
low which the wall is 
very smooth, so that an 
cannot escape. A fluid 
is secreted by the pitcher, which partially fills it, 
