LIGHT MICROSCOPY 1717 



directly, but only after slight preliminary swelling with KOH (1%); after 

 this pretreatment the grana, stained with neutral red at pH 7, appeared 

 dark red; they were then seen still forming columns (if viewed sideways), 

 but the distance between the grana in each column appeared wider the more 

 prolonged the swelling. 



From these experiments, Strugger derived the hypothetical model of a 

 chloroplast reproduced in figure 37A.2, showing carrier lamellae, grana im- 

 bedded in them, and columnar arrangement of the latter. He was certain 

 that each chloroplast is surrounded by a proteinaceous membrane, cjuoting, 

 in support of this \iew, the observed formation of ^'acuoles inside the 

 chloroplasts, and the separation of the membrane from the chloroplast 

 content in some pathological conditions. 



In connection with this model of the chloroplast, Strugger (1950, 1951) 

 developed a theory of the morphogenesis of the chloroplasts and grana, 

 according to which they develop from amoeboid "proplastides," containing 

 a single "plastidogen disc"; the chloroplasts arise by division of this 

 "gene-like" body, which is followed by the division of the stroma. In the 

 metamorphosis of the protoplastid into a mature chloroplast, the "plastido- 

 gen" disc divides into grana, which fill up the chloroplast body. 



Strugger believes that the grana-carrying laminae, although colorless, 

 are distinct from the— also colorless— stroma, and that the photosynthesis 

 proper is associated with the laminae, while the starch synthesis takes 

 place in the stroma; he referred in this connection to the work of Schmidt 

 (1951), showing that photosynthesis can contimie even when the stroma 

 is swollen by osmotic pressure, and the lamellae separated from each 

 other. 



Rezende-Pinto (1948, 194!), 1952''2'3) developed, also from light microscopic ob- 

 servations, u different picture of chloroplast structure: he placed all grana in a single 

 band— a "chioroplastoneme" winding, as a spiral, around the inner core of the chloro- 

 plast containing the stroma and starch grains. Several such bands were postulated to 

 exist in elongated chloroplasts (e. g., those of Spirogyra). These pictures were said to 

 interpret satisfactorily the observed birefringence of the chloroplasts. 



However, electron microscopic evidence clearly shows that grana are 

 distributed throughout the whole body of the chloroplast. One ciuestion 

 which seems to have been clarified by the above described (and other) 

 microscopic observations is the distribution of chlorophyll between the 

 grana and thestroma. In Chapter 14 (section A2) we mentioned that micro- 

 scopic observations indicated the concentration of chlorophyll in the grana, 

 but that sometime the stroma also appeared colored— perhaps by scat- 

 tering, .lungers and Doutreligne (1943) observed that in faintly green, 

 starch-filled chloroplasts, with only a single layer of grana visible against 

 the background of starch, green coloration was clearly restricted to the 



