114 



Mary Gordon 



and of a barley grain (Text Fig. IX.). With the exception of 

 occasional cases in which dividing nuclei occur just beneath the 

 superficial cambial layer, no cell divisions take place in the 

 starchy portion of the endosperm, which is entirely derived 

 from segment cells cut ofif from the cambium. 



Text Figure IX, 



Transverse section of ripe barley grain. 



A — Pericarp. 



B— Testa. 



C— Aleurone layer several cells deep. 



D — Endosperm (starch). 



The fact that the aleurone layer differs from the starchy 

 endosperm in being a resting layer, enables us to understand 

 several of its peculiarities. Thus Stoward (6) has shown that 

 the removal of the aleurone layer from the endosperm lead's" 

 to a marked fall in the output of carbon dioxide by the grain, 

 and indicates approximately the comparatively large share of 

 the total respiratory output that is due to the aleurone layer. 

 Injury to the seed alone would tend to cause an increased 

 respiratory activity manifested as a wound reaction. Although 



