Chapter 37 

 MISCELLANEOUS ADDITIONS TO VOLUMES I AND 11,1 



When this chapter was first planned, it was intended to described in it 

 the various new developments, in the fields covered in Volumes I and II, 

 1, which were not extensive enough to warrant treatment in separate 

 chapters (as did the two topics discussed in chapters 35 and 36). By the 

 time of the final revision of the text, however, some of these subjects had 

 grown so much that devoting a separate chapter to them would have been 

 quite appropriate, but cross references in previous volumes made rear- 

 rangement impossible. 



Since parts A and B below are more in the nature of independent chap- 

 ters than subdivisions of a single one, the bibliography follows each part, 

 instead of being collected at the end as in the other chapters. 



A. Structure and Composition of Chloroplasts, 

 Chromoplasts and the Chromatoplasm* 



(Addendum to Chapter 14) 



1. Light Microscopy 



Despite its much lower magnification, light microscopy retains one 

 advantage over electron microscopy — the possibility of observing the cell 

 in its natural state, without maceration, desiccation, or chemical treat- 

 ments unavoidable in the preparation of objects for electron microscopy. 



In chapter 14 (pp. 358-363), it was reported that microscopic ob- 

 servations of chloroplasts, in visible and ultraviolet light, have revealed the 

 presence, in most of them, of round, flattened dark bodies designated as 

 grana, about 0.5 m in diameter (Heitz, fig. 39a). In some cells, however 

 the chloroplasts seemed to consist of continuous bands — designated as 

 lamellae — without clear evidence of granular structure (Menke, fig. 41a). 

 Menke suggested that the grana may be, ciuite generally, only bulbous 

 parts of the lamellae, as illustrated by schematic figure 41b. 



We will see in the next section that for a while electron microscopy 

 has centered all attention on the grana and the stacks of thin lamellae or 

 discs of which these bodies appear to be constructed. More recently, 

 however, several observers have obtained electron micrographs, of sec- 



* Bibliography, page 1775. 



1714 



