5 CHLOROPLASTS 243 



cell division (E. B. Harvey, 1936). If, on the other hand, portions of 

 chromosomes are removed from the nucleus while division is going 

 on, the result is a serious modification of the hereditary process. 



Although the cytoplasm is able to build up very complicated 

 molecular systems, its architectural capacities are to some extent 

 limited, for it cannot produce from itself the protein structures of 

 nuclei and plastids. In heterotrophic organisms it even lacks the 

 capacity to manufacture relatively simple elementary units, which are 

 needed for protoplasmic synthesis; it is for this reason that these 

 compounds have to be added as vitawins to the culture medium 

 (ScHOPFER, 1936/37). 



As a rule, all such problems are studied in their purely chemical 

 aspect. Yet the molecules should not be considered only as chemical 

 supporters of reactions, but also morphologically as elementary units 

 of the high polymeric gel frame. In the cytoplasm, this texture is very 

 finely spun, is labile and is involved in permanent reconstruction. 

 In the chromosomes of the nucleus, on the contrary, it has far greater 

 density and a certain stabiHty and is therefore distinct from the cvto- 

 plasm, not so much on chemical as on structural grounds. 



§ 3. Chloroplasts 



a. Microscopic Structure of the Chloroplasts 



According to the handbooks of Schurhoff (1924, p. 57), Guil- 

 LiERMOND, Mangenot et Plantefol (1933, p. 1 5 8), Sharp (1934) and 

 KiJSTER (1935a, p. 288), the chloroplasts are microscopically homo- 

 geneous. They are described as hydrogels and both Kuster (1935a) 

 and HoFMEiSTER (1940) even incline to the view that they are in a 

 liquid state of aggregation, though their flattened shape and their 

 autonomic transfiguration (Senn, 1908) would discount this view. As 

 against Kuster's presentation of the matter (1935 a), richly docu- 

 mented as it is, publications have been amassing since 1935 arguing 

 in favour of a microscopic structure in living chloroplasts (Hubert, 

 1935, p. 369; DouTRELiGNE, 1935; Heitz, 1936a, b; Frey- Wyssling, 

 1937c; Geitler, 1937; Weier, 1938). All the investigators mentioned 

 find the chloroplasts to be finely granulated and for this reason appeal 

 to Schimper's (1885) and A. Meyer's (1883) grain theory. Schimper's 



