1722 CHLOROPLASTS, CHROMOPLASTS AND CHROMATOPLASM CHAP, 37A 



r.p.m. By resuspendiiig in 10% sucrose solution and precipitating several 

 times in a slow-speed centrifuge, a material consisting of intact, whole 

 cbloroplasts could be obtained. Figure 37A.4 (Vatter 1952) is similar to 

 those of Algera et al., showing shadowed grana in a whole chloroplast. 

 Figure 37A.6 is a shadow-cast preparation of a disintegrated chloi'oplast, 

 showing grana — flat cylinders about 0.() n in diameter. Figure 37A.7 rep- 

 resents the stroma ("matrix") material, photographed with a higher mag- 

 nification, and revealing, in the "blebs" and scattered all over the film, 

 small spherical granules about 0.025 n in diameter. According to Vatter 

 (1952), these globular molecules vary in size from 10 to 50 m^t, depending 

 on the solvent used in the extraction of lipides. 



Algera et al. suggested that the "lamellae" or "blebs" are similar to, or 

 identical with, the "myelin tubes" observed under the light microscope in 

 whole chloroplasts and illustrated in figure 47 in Volume I (p. 375) ; the 

 latter had been interpreted as swollen phosphatides. Algera et al. pointed 

 out that the "blebs" often are larger in diameter than the original chloro- 

 plast, and thus must be artefacts. 



However, one has to be careful and distinguish between the many differ- 

 ent thin objects seen in the electron micrographs of chloroplasts. Some of 

 these objects are folded, others smooth; some granular, others uniform; 

 some large and varied in size and shape (usually round or oval, but some- 

 times streaky or fibrous), others small and uniform in size. The only thing 

 they have in common is that they are thin compared to the grana. 



The very large, folded objects may be chloroplast membranes, fi'om which 

 the content has leaked out. Frey-Wyssling and Miihlethaler (1949) pub- 

 lished electron micrographs (of tobacco chloroplasts) showing all grana en- 

 closed in a large, folded membrane bag. They pointed out that, to form 

 folds, this membrane must be half-solid, /. c, a gel. It may be formed by 

 fibrous proteins; Thomas, Bustraan and Paris (1952) noted that chloro- 

 plast membrane bags remain whole after extraction with benzene, and that 

 fragments of them are visible after digestion with lipase. They suggested 

 that the chloroplast membrane — similar to the erythrocyte membrane — 

 consists of a "skeleton" of fibrous proteins supporting a delicate lipide 

 "epilemma." 



However, Vatter (1952) could obtain folded membranes only in prepara- 

 tions fixed with osmic acid (fig. 37A.5), or exposed to concentrated buffers, 

 and suggested that they are precipitation artifacts. 



The same opinion was expressed by Leyon (1953\ cf. below) and later 

 also by Frey-Wyssling and Steinmann (1953). The latter pointed out that 

 even if the folded bags, which on some micrographs seem to enclose all 

 grana, prove to be artifacts formed when the outer layer of the stroma comes 

 in contact with a changed medium (such as distilled water), this does not 



