23 



THE FRUIT. 



The husk or shell, composed of the ovary wall and the 

 remains of the two ovular integuments, is closely adherent 

 to the endosperm, which becomes differentiated into two 

 distinct portions (Fig. 3). The outer consists of a single 

 layer of large, somewhat brick-shaped cells arranged end 

 on to the lining of the seed. They contain large numbers 

 of minute rounded aleurone grains, the nitrogenous food 

 material. The aleurone layer encloses on all sides, except 

 that occupied by the adjacent surface of the scutellum, the 

 great mass of starchy endosperm, the flour of domestic 

 use. The latter is contained in large thin-walled paren- 

 chyma cells and within the vacuoles of their now scanty 

 cytoplasm. The nucleus is still usually present. The 

 starch grains of the endosperm are spherical with a central 

 hilum, and the concentric arrangement of their body 

 substance around that point gives them the characteristic 

 cereal-starch form. 



The scutellum surrounding the embryo is formed of 

 the basal part of the cotyledon, and that portion lying 

 against the floury endosperm functions in breaking down, 

 absorbing, and transferring its contents to the seedling 

 plant on germination. It acts in like manner on the single 

 layer of aleurone endosperm where they come into contact. 



The morphology of the endosperm is a difficult 

 question, but its functions are closely connected with the 

 nutritive aspects of the alternation of generations, in which 

 the sporophyte or asexual form of the plant and the 

 gametophyte or sexual form succeed each other in the 

 life-cycle. The endosperm is at first accompanied by the 

 unusual development of antipodal cells, which are separated 

 from all other contents of the embryo-sac by the formation 

 of walls around them. Outside the sac in numerous plants 

 other reserves of food material derived from the nucellus, 



