1720 CHLOROPLASTS, CHROMOPLASTS AND CHROMATOPLASM CHAP. 37A 



metal shadowing), the residue presented a picture similar to that shoAvn in 

 figure 37A.3. The darker grana (about 40-60 of them are present in spinach 

 chloroplasts, about 50-200 in maize chloroplasts, used in fig. 37A.3) are 

 rather uniform in shape and size; they are embedded in a less dense "stroma." 

 Shadowing (deposition of a thin film from a parallel stream of heavy 

 metal atoms impinging on the specimen under an angle) clearly shows the 

 greater thickness of the grana as compared to the matrix (see fig. 37A.4). 



Fig. 37A.6. Electron micrograph of grana of maize (shadowed). 

 Note the different thicknesses of the grana, which seem to bear no rela- 

 tion to their diameter. (Perhaps the thinner bodies are residues from 

 partially scattered grana.) (After Vatter 1952.) 



From the angle of shadow cast and the length of the shadow, the height 

 of the grana can be estimated as being of the order of 0.1 ii (0.05-0.30 n) ; 

 their average diameter is about 0.6 n. (It should be kept in mind that these 

 are dimensions determined in the dried, and therefore more or less shrunken, 

 state.) 



Granick and Porter's photomicrographs showed, in addition to grana, 

 also round or oval, partly folded "blebs," which they thought consisted of 

 vacuolated and collapsed stroma material. Figure 37A.5 shows these 

 forms in maize chloroplasts. 



Washing a chloroplast film with methanol visibly leaches out the pig- 

 ments—and probably other lipophilic materials as well. Under the electron 

 microscope, leached grana appeared to Granick and Porter to have lost 

 much of their density and to have shrunk considerably, thus confirming 



