MITOCHONDRIA 173 



tion. Considerable changes now occur in the scutellum : the cells 

 elongate and increase in size, there is also considerable crushing 

 of the depleted endosperm cells, and the elongated cells of the 

 scutellum may form themselves into hypha-like growths which 

 invade the endosperm. 



Horning and Petrie also studied the behaviour of the mito- 

 chondria in the resting grain in both scutellum and endosperm. 

 They were found to be present in moderate amount in the epithelial 

 cells and other cells of the scutellum, and were but sparsely distri- 

 buted in the endosperm. The material was examined three days 

 after the onset of germination, when the endosperm cells imme- 

 diately adjacent to the scutellum had begun to show signs of 

 depletion. In the meantime the epithelial cells, as well as the 

 rest of the cells of the scutellum, had greatly increased in size, 

 causing considerable crushing of the depleted cells of the endo- 

 sperm. The scutellum now showed a great profusion of mito- 

 chondrial bodies, which were located in all the cells of the 

 scutellum and epithelium. These bodies were found to be clustered 

 in particularly large numbers round the outer walls of many of 

 the epithelial cells, often appearing to be partly embedded in the 

 cell wall itself. Horning and Petrie suggested that this feature 

 shows that the mitochondria have actually passed through the 

 epithelial layer into the endosperm. Presumably the mito- 

 chondria arise in the epithelium by repeated division. Six days 

 after germination had commenced, they were found to extend 

 well into the endosperm cells adjacent to the epithelium which 

 were in the process of undergoing depletion of their starch 

 content. Numbers ot these mitochondrial bodies clustered round 

 the walls of the endosperm cells, and in many cases they were 

 actually found to be surrounding the grains themselves. Starch 

 grains enclustered in this manner were always discovered to 

 be in an advanced stage of erosion, while those which were not 

 so far corroded invariably had fewer chondriosomes surrounding 

 them. Horning and Petrie considered that some of the mito- 

 chondrial bodies present in the endosperm were certainly formed 

 in situ, but that this supply was continuously being supple- 

 mented by an active process of secretion from within the epithe- 



