260 



VEGETABLE PHYSIOLOGY 



ing to the natural orders Capparidacea and Tropaolacea, 

 the glandular cell divides several times to form a little mass 

 or nodule of secreting cells, which must be regarded as a 

 rudimentary gland, though it is not provided with any 

 definite outlet or duct. 



In the seed of the cereal grasses there is a special 

 organ separating the embryo from the endosperm. This 

 structure, which is a modification of part of the cotyledon, 

 is known as the scutellum (fig. 123) ; its function is to effect 

 the absorption of the nutritive material of the endosperm, 

 and supply it to the growing embryo. This scutellum is 

 covered on it's outer face, which is in contact with the 



FIG. 123. SECTION OF OAT-GRAIN. 

 p, plumule ; r, radicle ; s, scutellum. 



FIG. 124. SECTION OF PORTION OF 

 SCUTELLUM OF BARLEY, SHOWING 

 THE SECRETING EPITHELIUM. 



endosperm, by a layer of cylindrical cells, whose long axis 

 is at right angles to the surface (fig. 124). These cells' are 

 very granular in appearance, and form a very marked 

 secreting structure, producing two enzymes, which are sub- 

 sequently discharged into the endosperm to effect the diges- 

 tion which must precede absorption. The aleurone layer of 

 the same grain (fig. 125), which has already been described, 

 is also a secreting layer, resembling the outer layer of the 

 scutellum in several respects. 



The tentacles of the leaves of Drosera, to which allusion 

 has already been made, are very definitely secreting 

 structures ; in addition to preparing an enzyme they pro- 



