174 BOTANY 



Hum. They suggested that diastase is secreted from the scutellum 

 in association with the mitochondria, and that in this manner the 

 enzyme is brought into contact with the starch grains, and that 

 active hydrolysis ensues. 



Although mitochondria were also found to be present in the 

 aleurone layer of the grains, no evidence was found for their 

 migration from this region into the endosperm cells. Examination 

 of the isolated endosperm mounted in " plaster of Paris " pillars 

 immersed in water showed that in sixteen days the number of 

 mitochondria was distinctly greater than in the dormant grain 

 They occurred in clumps scattered throughout the cells, and were 

 also observed in the elongated form and in process of fission. It is 

 therefore evident that mitochondria can increase in the endo- 

 spermal region without active secretion supplementing the supply 

 from the epithelial layer and scutellum. The rate of hydrolysis, 

 however, in the isolated endosperm was very much less without 

 secretion from the scutellum. Similar results were obtained in 

 barley and wheat, but in these cases there was also a simultaneous 

 secretion of a cytohydrolytic enzyme which dissolved the walls of 

 the endosperm cells prior to the hydrolysis of the starch grains. 



It is feasible that mitochondria should be able to migrate 

 through the plasma-membrane. Cowdry, for example, has con- 

 cluded that mitochondria are for the most part phosphatides in 

 composition, together with the addition of a small amount of pro- 

 tein, and there is sufficient evidence to show that fattv substances 

 of various kinds pass from apical meristems, where they are syn- 

 thesised, into external differentiating cells, in the course of which 

 translocation through numerous cell walls must occur. 



The Vacuome 



The presence of vacuoles filled with cell sap is a well-known fact 

 in plant cells. These vacuoles differ in size in different cells. In 

 meristematic tissues they are small and numerous, and as these cells 

 grow and differentiate, they increase greatly in size and coalesce. 

 The vacuolar system of a cell, whether there be a single or many 

 vacuoles, has been termed by Dangeard the " vacuome.''^ 



The origin of the vacuolar system, or vacuome of cells has 



