23.] 



CHAPTER I. THE CELL. 



i\ 



wall of a vesicle (Fig. 52). Bat starch-grains may be formed in a 

 chloroplastid, as in a leucoplastid, in the absence of light; the 

 organic substance required for the building-up of the starch-grain 

 being not produced in the chloroplastid itself, but supplied from 

 other parts of the plant. 



These plastids are termed chloro- 

 plcustids, because the colouring-matter 

 upon which their assiruilatory func- 

 tion depends is most commonly the 

 familiar green colouring-matter, chlo- 

 rophyll. But they are not always 

 green. In some of the Algae they are 

 red or brown, because in addition to 

 chlorophyll there is present in the 

 one case (Rhodophyceae), a red 

 colouring-matter, phycoerythrin, and 

 in the other (Phaeophyceae) a brown, 

 colouring-matter, pltycoxanthin. Both 

 these substances are, however, re- 

 lated to chlorophyll. 



FIG. 52. Isolated cliloroplastids with 

 starchy contents from the leaf of Funaria 

 hygrometrica(55Q). a A young corpuscle; 

 b an older one, b' and b" have begun to 

 divide; cde old corpuscles in which- the 

 starchy contents fill almost the whole 

 space ; / and g after maceration in water 

 by which the substance of the corpuscle 

 has been destroyed and only the starchy 

 contents remain. (After Sachs.) 



FJG. 53. Cladoyhora glvmerata 

 (after Strasburger : x 540). A 

 ccenocyte of the filament (chromic 

 acid and carmine preparation) : 

 n nucleus; ch chloroplastid; the 

 polygonal chloroplastids form a 

 continuous layer, the outlines of 

 the individual plastids remaining 

 visible ; p pyrenoids ; v starch- 

 grains. 



When the colouring-matter is dissolved out by alcohol or some 

 other solvent, the protoplasmic plastid is left colourless, but un- 

 changed in form or size. The chlorophyll appears to exist in an 



