172 BOTANY 



plasts. For a description of the recent papers on this aspect of 

 the problem, see Barton-Wright, " Recent Advances in Plant 

 Physiology." 



As well as their probable function of plastid formation, a number 

 of other views have been put forward with regard to their activity 

 in the cell, and some of the more important of these will now be 

 discussed. 



According to Marston, from the reactions of mitochrondia to 

 azine dyes, these bodies contain proteolytic enzymes, and he 

 came to the conclusion from the rapidity with which synthetic 

 processes occur in the living cell, that the mitochondria are the 

 site of enzymatic synthesis in the cell. Robertson held that the 

 presence of lipoid material in these bodies would cause molecules 

 to be orientated at the surface in such a manner that the reactive 

 groups (carboxyl and amino-acid) would point to the external 

 aqueous phase, and so be effectively concentrated at the phase 

 boundary of mitochondrium and cytoplasm. According to both 

 de Nouy and Cowdry, mitochondrial substance is arranged in 

 such a manner as to give a surface film of maximum extent with 

 the minimum of material, and such a local concentration would 

 furnish an explanation of the facility with which enzymatic syn- 

 thesis would take place at the surface of these bodies in the cell. 



Horning and Petrie have investigated the influence of mito- 

 chondria on starch grains present in the endosperm of cereals. 

 The types used were Red Hogan maize. Warden wheat and Cape 

 barley. Hand-stained sections were prepared and stained in 

 Janus Green B (1 in 8,000). This dye was found to be excellent 

 for the purpose of rendering the mitochondria visible. The 

 material was also fixed in osmo-chromic fluid and Cox's fixative. 



It is a well-known fact that in maize the endosperm is packed 

 with starch grains, and that at the onset of germination the finely- 

 granulated cytoplasm of the epithelial cells of the scutellum be- 

 comes coarser in structure and this granulation increases in amount, 

 following on the erosion of the starch grains in the endosperm cells 

 adjacent to the epithelial cells bounding the scutellum. The hydro- 

 lysed products of the endosperm cells are absorbed by the epithe- 

 lium, and are then passed on to the embryo and used in germina- 



