82 GRASSES OF IOWA. 



that of the scutellum; they can therefore be seen only in tan- 

 gential and not in radial section of the seed. In germination, 

 each rootlet independently breaks through the coleorhiza, 

 which surrounds each with a smaU sheath. Before the roots 

 break through, the elongating coleorhiza ruptures the pericarp 

 and sends numerous hairs from its epidermis, thus fastening 

 the somewhat superficially placed seed to the ground. 



Physiology of germination. — It may be interesting now to dis- 

 cuss the physiological process of the germination of grass 

 seeds. The food material made by the leaves is deposited in 

 the seeds in the form of reserve material, consisting of two 

 classes of substances, the albuminoids and carbohydrates. 

 The amounts of these vary in different species. The manner 

 in which the albuminoids are deposited varies, but they occur 

 largely in the form of proteids, deposited in the form of 

 aleurone grains. 



The carbohydrates occur largely in the form of starch, 

 though in some few cases reserve cellulose occurs, as la the 

 perisperm of the seed of Bromus and allied grasses. An exam- 

 ination of the endosperm of grass seeds indicate that the outer 

 layer of the endosperm consists of cells that differ in a marked 

 way from the remaining cells. The researches of Haberlandt 

 and several other writers have shown beyond a doubt, that 

 this layer is a secreting organ in which ferments are produced 

 which are transferred to the remainder of the endosperm, 

 where the starch is converted to a sugar where it is taken up 

 by the cylinder absorption epithelium, the outer row of cells of 

 the scutellum. 



The wide and universal distribution of the aleurone layer 

 would appear to indicate some physiological purpose. Its 

 function has been nicely demonstrated by Haberlandt and 

 other writers. 



Brown and Morris,* who have studied the germination of 

 barley and a few other grasses, differ in regard to the digestive 

 action of the aleurone cells. Haberlandt 's work was carried 

 out with rye, and as stated above indicate that the aleurone 

 layer is a diastatic secreting tissue and that the aleurone layer 

 does not entirely belong to the reserve food system. Haber- 

 landt found the corrosion of starch grains first look place 

 between the scutellum and the aleurone layer on the ventral 

 side and this corrosion rapidly extended to the starch grains 



♦Jour. Ohem. 8oc. London. 57: 458. 



