1/32 CHLOROPLASTS, CHROMOPLASTS AND CHROMATOPLASM CHAP. HI A 



this time on Aspidistra elatior, produced a very beautiful seciuence of 

 pictures, showing first a few folded lamellae which rapidly multiply into a 

 packed group and finally fill the whole chloroplast, which then appears 

 Hke a carefully combed wig. The grana appear in these chloroplasts only as 

 more or less clearly outlined areas, of circular cross-section, in which the 

 striation is accentuated by greater thickness of the lamellae and greater 

 regularity of their parallel arrangement. The lamellae continue into the 

 intergranular space, where single lamellae often become paired into double 

 sheets. * 



Thomas (1954) suggested that "giana free" ehloroplasts should be considered as 

 single, giant grana. 



The ciuestion of the origin of grana — as well as of the chloroplast as a 

 whole — is in need of more study; the surmise that "chloroplasts arise only 

 by division of chloroplasts, and grana only by division of grana," is by no 

 means established (and in the case of grana, most likely incorrect). We 

 cannot enter here into these problems of cytogenetics and morphological 

 differentiation (c/., for example, their review in the article by Weier and 

 Stocking, 1952). 



We must now say a few words on the so far rather neglected subject of 

 the structure of the stroma. It was stated above that it seems to consist 

 of lipoproteids, not stainable by lipide-soluble dyes, and to give rise, upon 

 swelling to ''blebs," "pancakes," and "myelin figures," of widely varying 

 size in which numerous spherical macromolecules (probably, lipoproteids) 

 remain imbedded. Under certain conditions, the stroma can produce also 

 fibrillar proteinaceous structures, first observed by Thomas et at. (1952) in 

 the stroma of spinach chloroplasts after the removal of lipoids by acetone 

 extraction or digestion by lipase. 



Bustraan, Goedheer and Thomas (1952) found that these structures — similar to 

 those observed in certain cytoplasmic preparations — consist of beads ("chromidia") 

 about 0.12 M in diameter, strung together on threads ("interchromidia"). Bustraan 

 et al. measured the optical density of the "chromidia" and "interchormidia" on non- 

 shadowed micrographs, and their thickness on metal-shadowed micrographs, and con- 

 cluded that the material of the chromidia is denser by about Vs (after acetone treat- 

 ment) or V2 (after lipase treatment) than that of the interchromidia. 



In Frey-W^ssling and Steinmann's (1953) electron micrograph of a 

 cross section of a fixed tulip chloroplast, laminar grana are seen imbedded 

 in a granular stroma. (As mentioned above, no carrier laminae, postu- 

 lated by Strugger, are noticeable on this photograph, and the arrangement 

 of the grana does not suggest their existence.) 



Frey-Wyssling and Steinmann noted that the stroma has a much 



* Results obtained with new methods of fixation and sectioning, and clearly showing; 

 the relation of granular to laminar structures, are briefl\- reported on p. 1986, cf. Figs. 

 38.1-38.4. 



