406 



ECOLOGY. 



and delightful to study. At the entrance (figure 497) a broad 

 sweep of typha margins a projecting arm of the land which affords 

 a quiet nook for the repose of mats of green algae, of such sorts 



Fig. 499. 

 Pontederia, showing leaves and flower spike. 



as spirogyra, cedogonium, cladophora, etc., floating on the placid 

 water in the foreground. Slender stems of zizania rise like 

 shooting stars among the flags, with scirpus crowding near, 

 while masses of the flowers of the thoroughwort are sheltered by 



