THE CHLOROPLAST 97 



membrane. In the absence of chlorophyll, the lamellae are not 

 formed, although the eyespot, starch grains, and pyrenoid are still 

 found within the chloroplast membrane (Sager and Palade, 1957; 

 Sager, 1958). 



In the development of the chloroplast in flowering plants, the 

 first visible stages lack all the structural properties typical of the 

 fully developed chloroplast. Heitz (1955) and Leyon (1956) con- 

 clude from electron microscope studies that there is a primarv 

 granum that has a crvstalline structure. Whether such crystalline 

 bodies exist in the living state or whether their crvstallinity is en- 

 hanced by preparative techniques for electron microscopy is difficult 

 to decide. The crystalline structure of the primary granum, as 

 found in Chlorophijtum, Aspidistra, and other monocotyledons, is 

 also present in dicotyledons. This suggests that there must exist 

 some association between the crystalline lattice and the develop- 

 ment of the lamellae ( Heitz, 1955 ) . Miihlethaler ( 1959 ) has shown 

 that the lamellar structure develops from "tubules" or "cristae" anal- 

 ogous to mitochondria. Upon illumination, the cystalline structure 

 develops into a lamellar system as seen in the full-grown chloroplast 

 of Elodea canadensis ( Fig. 7a and b ) . It is indicated that here too 

 the formation of the lamellae proceeds parallel with the pigment 

 synthesis. 



Von Wettstein investigated the relation of gene action to the sub- 

 microscopic structure of the chloroplasts by employing chlorophyll 

 lethals of barley (von Wettstein, 1957a, 1957b, and 1958). In the 

 development of the barley chloroplast, there is an undifferentiated 

 proplastid with a center core; starch grains accumulate, lamellae are 

 formed, and the plastid as a whole becomes trans versed by lamellae. 

 In an albino type, essentially normal early proplastids enclosed by 

 a double membrane were found. There is no differentiation of 

 ordered layers, lamellae, or grana. Differentiation does not proceed 

 beyond the earliest stages, but the plastid increases in size to that 

 of a full-grown chloroplast. The gene change has blocked the de- 

 velopment of the submicroscopic chloroplast structure at an early 

 stage, but not the growth of the plastid as a whole. Instead of the 



Fig. 7. Electron micrographs of (a, b) developing chloroplast in Elodea 

 canadensis, a higher plant, showing (a) crystalline structure and (b) fully 

 developed chloroplast (Courfesy, Dr. K. Muhlethaler, Eidgenossische Technische 

 Hochschule, Zurich), (c) Chloroplast of Poteriochromonas stipitafa, a chryso- 

 moncd. 



