BIREFRINGENCE OF CHLOROPLASTS 



365 



0.01-0.02 /i. Kausche and Ruska agreed with Menke that these laminae 

 may be of an even more fundamental importance for the structure of 

 chloroplasts than the grana. 



The suhmicroscopic .structure of chloroplasts was also investigated by Roberts 

 (1940, 1942). Using an optical microscope, she observed first the presence in the 

 chloroplasts of various species of ferns, thallophytes, bryophytes, and spermaiophytes of 

 a small number (e. g., 3 or 4) of "plastidules" into which a chloroplast can easily dis- 

 integrate, each plastidule containing several (4-40) "granules" about 1 ^i in diameter 



Fig. 44. — Birefringence of chloropla.sts. a: Mougeotia, the end walls of the cells, 

 and the chloroplasts (seen in profile) are bright; b: Closterium lunula (after Menke), the 

 chloroplast, in particular its ribs, is bright; c: Anthoceros (after F. Weber), gametophyte 

 cells, each containing one clioroplast, are bright at the upturned edges of the latter 

 (from Schmidt 1937). 



(these were probably identical with the Heitz grana). In a subsequent study with the 

 electron microscope, the granules were found to consist of "primary," "secondary," 

 "ternary," "quaternary," and "quintary" subunits, whose sizes were 0.4-0.5, 0.25, 0.1, 

 0.04 and 0.02 a(, respectively. Figure 43 shows a chloroplast of Elodea canademtis, 

 magnified 10,000 and 100,000 times, revealing "subunits" of difTerent order. The 

 relation between these subunits and the laminae shown in figure 42, is not clear. 



4. The Birefringence of Chloroplasts 



It has been mentioned above that the laminar structure of the chloro- 

 plasts was first postulated as a means of explaining their double re- 

 fraction. 



The birefrigency of chloroplasts was discovered by Scarth in 1924 and 

 rediscovered by Kiister (1933, 193G), Menke (1934), and Weber (193(j). 



