DIGESTION 



258 



(fig. 122) and the secreting structures of the leaves of Dioncea 

 and other plants, as well as the similar bodies which occur 



Fia. 121. SECTION THROUGH EXTERNAL REGION OF GRAIN 

 OF BARLEY. 



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

 containing aleurone grains ; am, cells of endosperm ; 

 TO, nucleus. (After Strasburger.) 



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 consist of a few 

 cells situated on a stalk, are found in 

 great numbers on other plants, especi- 

 ally 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- 

 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 



FIG. 122. GLANDULAR 

 APEX OF A TENTACLE 

 OF Drosera. 



