42 



PROTOPLASM 



the moss Schistostega osmundacea (Fig. 34). This small moss 

 lives in the deep recesses of rocks, usually in caves where the light 

 is weak. Just why it "chooses " such dark places cannot be said, 

 but since it apparently does "prefer " them, it is fortunate that its 

 cells are such excellent optical systems as to collect the feeble light 

 and focus it on the chloroplasts. Each cell of the protonema is a 



Fig. 34. — Schistostega osmundacea; a, the entire moss, b, a single cell. 



lens at the base of which the few chloroplasts are situated (Fig. 

 346). Light enters at the top and is focused on the chloroplasts, 

 thus concentrating the little sunlight available for photosynthesis. 

 The light is totally reflected after passing through the chloroplasts 

 and thus acquires a green phosphorescent tinge, so that the moss, 

 when seen deep in the moist crevice of a rock, resembles the 

 eyes of a cat at night. 



Such are cells; with these and the matter that fills them does 

 this book deal. 



