356 



CHLOROPLASTS AND CHROMOPLASTS 



CHAP. 14 



plasts can evolve oxygen from water in light, but are unable to use 



carbon dioxide as oxidant in this reaction, agrees well with this hj^pothesis. 



The chromoplasts of the algae are of varied size and shape, e. g., stars 



(Fig. 37c), bands (Fig. 37d), or discs (Fig. 37a and e); giants with 



p — 



Fig. 37. — Chromoplasts (c) and pyrenoids (p) in algae, a. Disc-shaped chloro- 

 plasts (Eremosphaera, after Moore); b. Division of a pyrenoid {Zygnema pectinatutn, 

 after Czurda); c. Star-shaped chlorop lasts (Prasiola); d. Band-shaped chloroplast; 

 e. Disc-shaped chloroplasts in a diatom {Cocconeis placeniula Ehrenb.). (AU drawings 

 except d from Fritsch 1935.) 



linear dimensions up to 100 ^ have been observed in some species. 

 ChloreUa, the unicellular green alga widely used in the study of photo- 

 synthesis, contains a single, bell-shaped chloroplast which covers the 

 inside of the cell walls, leaving only a narrow entrance into the interior 

 of the cell. 



