300 



RADIATION BIOLOGY 



rather indefinite particles, leading to "chlorophyll grains" of various 

 shapes. It was later recognized that they are specifically differentiated 

 parts of the protoplasm, and their genesis, especially in developing cells 

 of higher plants, was carefully studied by von Mohl and by Gris (see 

 Sachs, 1874), Hofmeister (1867), and others. Sachs stressed that extrac- 

 tion of chlorophyll by lipophilic solvents demonstrates that chloroplasts 



! 



I 



Fig. 5-1. An early picture of chloroplasts (Chlorophyllkdrnchen: grains of chlorophyll) 

 in the leaf of Vallisneria spiralis. (From Schleiden, 1845.) 



consist of two parts: the pigment and its protoplasmic bearer, a distinc- 

 tion that had been made earlier by Treviranus in 1814 (cf. Zirkle, 1926). 

 Sachs (1874, p. 46) states that chlorophyll is present in only minute 

 amounts and that, after extraction, the protoplasmic part keeps its shape 



and volume as "a solid, soft body which contains at 

 best small vacuoles and in which the coloring matter 

 sometimes is unequally distributed." Meyer in 1883 

 and Schimper in 1885, as is well known, first advo- 

 cated a structure with dark "grana" in a lighter- 

 colored "stroma," but for a long time the common 

 opinion was that chlorophyll is homogeneously distri- 

 buted in the chloroplast. According to Weier (1938), 

 healthy and vital chloroplasts may be either granular 

 or homogeneous. About 1935 the idea that chloro- 

 plasts often have a granular structure was revived, 

 especially by the work of Heitz (1936) and of 

 Doutreligne (1935). The latter presented photo- 

 micrographs of grana in chloroplasts in intact 

 leaves of water plants in their natural medium (Fig. 5-2). Frey-Wyssling 

 (1948) holds the view that in the chloroplasts, observed as homogeneous, 



Fig. 5-2. Grana in 

 chloroplasts of Ca- 

 bomba aquatica in 

 blue light. {From 

 Doutreligne, 1935.) 



