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 



FIG. 121. SECTION THROUGH EXTERNAL REGION OP GRAIN OF BARLEY. 



p, pericarp of fruit ; t, testa of seed ; al, layer of cells containing aleurone 



grains ; am, cells of endosperm ; n, nucleus. (After Strasburger.) 



the leaves of Dioncea 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 

 usually classified according to the mate- FlG- ^.-GLANDULAR 

 rials on which they work. We may 

 describe here four groups, the members 

 of which take part in the digestion of reserve materials, 

 as well as in the processes of external digestion. These 



APEX OF A TENTACLE 

 OF Drosera. 



