DIGESTION 
247 
duce a weak acid, both of which are present in the glairy 
material that they pour out over the captured insect. 
These tentacles (fig. 122) and the secreting structures of 
Fic. 121.—SrcTIoN THROUGH EXTERNAL REGION OF GRAIN oF BARLEY. 
p, pericarp of fruit; ¢, testa of seed; al, layer of cells containing aleurone 
grains; am, cells of endosperm; , nucleus. (After Strasburger.) 
the leaves of Diongea and other plants, as well as the 
similar bodies which occur in the lining of the pitcher of 
Nepenthes, must be regarded as actual glands, comparable 
to those of the alimentary canal of the 
animal body, though less complex in 
structure. Glandular hairs, which con- 
sist of a few cells situated on a stalk, are 
found in great numbers on other plants, 
especially some species of Saxifraga. 
There are many of these enzymes 
present in different plants, the function 
of some of which is still not understood. 
Many, however, have been investigated 
with some completeness. They are 
a 
(Baldr 
Wc Nea 
f AX i 
usually classified according to the mate- pe. 129 Granpunan 
rials on which they work. We may 
describe here four groups, the members 
APEX oF A TENTACLE 
or Drosera, 
of which take part in the digestion of reserve materials, 
as well as in the processes of external digestion. These 
