LIGHT MICROSCOPY 1715 



tioned chloroplasts of certain species showing a laminated structure ex- 

 tending througii the whole chloroplast, without grana, similar to Menke's 

 ultraviolet micrograph of the Anthoceros chloroplast in figure 41a. This 

 attracts new interest to the observation of chloroplasts under the light 

 microscope, where the relationship between granulated and laminated 

 structure can be studied under more nearly natural conditions and on a 

 much wider scale. 



The first ciuestion is whether it is true that the grana in granular chloro- 

 plasts are arranged in several planes parallel to the large cross section of the 

 chloroplast? If this is the case, is there evidence that the individual grana 

 are not independent bodies, but hang together as parts of a continuous 

 layer (which could be conceivably destroyed in the preparation of objects 

 for electron microscopy)? Heitz, the discoverer (or more properly, re- 

 discoverer) of the grana, saw them arranged in layers, giving the chloro- 

 plasts a laminated appearance when looked upon from the side (fig. 39c). 

 Similar layers are easily recognizable on some electron micrographs, c/. 

 fig. 37A.18. 



Strugger (1950) saw, in the exceptionally large chloroplasts of Dracaena, 

 that the grana, in addition to belonging to several distinct layers in the 

 "horizontal" plane, were also arrayed in "vertical" columns, one above 

 the other. This arrangement was confirmed, in a renewed study, in iso 

 lated chloroplasts from the same plant (1951). Plastids were suspended 

 in 0.2 M sucrose solution to prevent swelling; they could then be seen 

 clearly, under the light microscope, to contain green grana amidst a color- 

 less stroma. Strugger noted that moving the depth of the focus did not 

 change the position of the green spots — indicating that they formed verti- 

 cal columns continued through the whole depth of the chloroplast. The 

 same arrangement was directly visible in chloroplasts lying on their side; 

 selecti\'e staining of the grana with rhodamin B made the picture e\en 

 clearer. (It may be asked, however, whether the columnar arrangement 

 of the grana is a general rule; conceivably, it may be a response to intense 

 illumination, similar to the phototactic redistribution of whole chloro- 

 plasts in the cell.) When, in Strugger's experiments, water was substituted 

 for 0.2 M sucrose solution as the suspension medium, chloroplasts as were 

 seen to swell in the direction of the short axis, the columnar arrangement 

 of the grana was disturbed, and the plastids disintegrated into lamellae 

 which seemed to carry the grana in them. I^pon still further swelling, 

 the grana ceased to be visible. 



The same type of structure could be observed also in leaf sections con- 

 taining undamaged cells, with various Lilleiflorae, as well as with about 60 

 species from 59 other families. The "carrier lamellae" in which the grana 

 are imbedded, according to Strugger (like pills in cellophane sheets in cer- 



