244 FINE-STRUCTURE OF PROTOPLASM II 



doctrine states that the chloroplasts consist of a colourless stroma, in 

 which minute granules, lying on the boundary of microscopic visi- 

 bility, are embedded; and these contain the green pigment (Binz, 

 1892). Colloid research, however, had utterly refuted this view, for 

 the methods employed by colloid optics seemed to show that all living 

 components of the cells are fluid (Kuster, 1935 a, p. 290), optically 

 empty (Guilliermond, 1930) and microscopically homogeneous. 

 Consequently, any kind of microstructure made visible in some way 

 or other was said to be a form of precipitation, structure of coagu- 

 lation, artificial product or artefact. The granular structure of chloro- 

 plasts suffered the same fate. 



Photographs taken of living cells provided the evidence for the 

 refutation of the theory that the grains in chloroplasts are a product 

 of precipitation. The first microphotographic document may be said 

 to have come from Heitz (1932), who photographed chlorophyll grains 

 next to a living nucleus in the leaf stem of Victoria regia. Doutreligne 

 (1935) considers photography in red light an especially suitable means 

 of proving beyond doubt the inhomogeneous distribution of chloro- 

 phyll in the plastids. Her objects are mosses {Mniuw), Vallisneria, 

 Cahomha and Myriophyllum. Wieler (1936) identifies the grains in a 

 variety of Selaginella. But the most detailed work is undoubtedly that 

 of Heitz (1936a, b), which contains microphotographs of a great 

 number and variety of plants. The grains are decidedly identified in 

 mosses {Physcomitrium^ Hypnum, AInium, Funaria), vascular crypto- 

 gams, very many Monocotyledons and Dicotyledons. Most authors 

 preferred single-layer leaves, such as mosses and fern prothallia, for 

 their observations and Doutreligne avoids even the source of error 

 involved in the use of an embedding medium, using transparent 

 water-plants. Heitz disdains this precaution and includes sections of 

 living tissue in his investigations. One of the things he notices in the 

 leaf of Agapanthus umhellatus is that certain chloroplasts are liable to 

 be damaged (though the cause is not known) and in that state their 

 granular structure is far more clearly apparent than in the undamaged 

 specimens. Evidently this is a kindred case to the fixation of the 

 nuclei, where a barely visible structure in the live state is coarsened 

 in death and the blurred outlines of the optically merging structural 

 components become more sharply defined. Seeing that so many 

 observers have described the plastids as microscopically homogeneous. 



