ELECTRON MICROSCOPY 1 / '2'^ 



nates in the grana. However, estimates of the total amount of Hpide in 

 grana and in the stroma (cf. below) convinced Frey-Wyssling that this can- 

 not be true of all myelin; rather, a hirge part of it must come from the 

 stroma. The above-mentioned small granules, embedded in the "myelin" 

 masses, or scattered on the supporting film, are, according to Frey- 

 Wyssling, globular protein molecules, originally associated with the lipides 

 in the lipoproteinaceous stroma. 



The grana and the discs, into which they disintegrate, appeared as 

 the most striking — and potentially significant — structures in the photosyn- 

 thetic apparatus. It was therefore important to establish whether they 

 occur in all photosynthesizing organisms. 



Fig. 'MAA2. Irregularly shaped patches obtamed by sonic disinte- 

 gration of himinar chloroplasts of Spirogyra, fixed for 15 min. in 1% 

 Os04 {cf. Figure 37A.13) (after Steinmann 1952'). 



Thomas (1952) published electron micrographs .showing the presence 

 of grana in higher plants {Spinacia oleracea), green algae {Chlorella vulgaris), 

 blue-green algae {Synochoccus spp.), red algae (Porphyridium cruenium), 

 diatoms {Niizchia), purple bacteria {Chromatium D, Rhodo spirillum ruh- 

 rum), and green sulfur bacteria. The diameter of the grana reproduced 

 in his paper ranges from 1.3 m {Nitzschia), through 0.7 m (Porphyridium), 

 0.6 M {Chlorella, Syncechococcus), and 0.4 m {Spinacia}, to about 0.15 ^ in 

 bacteria. Another set of electron micrographs of material obtained from 

 the same organisms shows thinner, round bodies of the same diameter. 

 These are interpreted by Thomas as single protein discs from disintegrated 

 grana ; however, on some photographs (in particular, those of purple and 

 green bacteria), the distinction in thickness between the "grana" and the 

 "discs" is not very great, at least in the reproductions. 



Colorless bacteria showed no grana, but small grana were found in the 

 colorless alga, Proiotheca zopfii. 



