FINE-STRUCTURE OF PROTOPLASM 



II 



246 



proplastid divides and each part is provided with one of them. This 

 scheme of multipUcation goes on as long as there is cell division and 

 the number of proplastids increases in the young cells. Only when 

 their definite number has been reached and the cell differentiates do 

 the proplastids evolve to mature plastids. Then the self-reproduction 

 of the grana in the expanding plastid proceeds in a very characteristic 

 way. After splitting parallel to the disc-plane of the granule, the two 

 new platelets remain juxtaposed, split further and pile up, so that 

 cyHnders of grana result with their axes perpendicular to the surface 

 of the flat plastid. It is due to this arrangement that the green colour 

 of the grana is visible in the microscope in spite of their minute thick- 

 ness; in fact, it is not a single granule, but a pile of grana that is 

 observed. 



The grana produce chlorophyll only in the hght. If they contain 

 but a trace of this pigment, they can easily be discovered in the 

 fluorescence microscope. Before any chlorophyll is synthesized in the 

 proplastids, they must be made visible by staining with rhodamineB. 



b. Molecular Constituents of Ch lor op lasts 



Proteins, lipids and the pigments chlorophyll a, chlorophyll b, as 

 also carotene and xanthophyll, which are given the collective name 

 of carotenoids, go to the making of the chloroplasts. Menke finds 

 47.7% of protein and 37.4% of lipids in the chloroplasts of spinach 

 leaves. They are rich in ash (7.8%) and contain about 7.7% of chloro- 

 phyll (Menke, 1940b). Half the lipids consist of fats, 20% of sterines, 



TABLE XXIV 

 ANALYSIS OF CHLOROPLASTIC MATTER OF 



Spinacia ohracea 



IN % BY WEIGHT (rABINOVITCH, 1 94 5) 



