198 



Plant Physiology 



and form. It characterizes also to a very high degree the 

 algae and mosses, but it is absent from all the fungi. Sev- 

 eral facts regarding the habi- 

 tats and distribution of green 

 plants afford us an indication 

 of some of the conditions req- 

 uisite for the proper work 

 of plants thus endowed. The 

 presence of the green color 

 referred to is universally indic- 

 ative of the possession of 

 chlorophyll, a mixed pigment, 

 imbedded in certain chlo- 

 roplasts, or chlorophyll con- 

 taining bodies which are differ- 

 entiated portions of the living 

 protoplasm. In particular, it 

 is apparent that plants con- 

 taining this substance are sun- 

 loving or at least light-loving 

 organisms. They may grow 

 in partial shadow at times, but 

 they are wholly absent from 



FIG. 52. Cell of chlorenchyma 



all permanently dark or deeply showing chloroplasts with starch 

 shaded places. The large sur- ^ rains - [Adapted.] 

 faces of the leaves and the evident arrangement of these 

 and of the branches which bear them, with respect to light, 

 all indicate clearly a certain relation of green color with the 

 light factor. As the chief bearers of chlorophyll in seed- 

 plants the leaves command special attention, wholly aside 

 from their other functions or accessory work. Any agency 



