96 



LIVING PLANTS 



pond weeds, bladderworts and stone worts 

 which root in the mud at a few feet below the 

 surface. With the approach of aatumn the 

 tips of the stems grow in the form of a thick 

 shoot with short, crowded leaves which are 

 termed hibernacula. The hibernacula finally' 

 break loose from the stem, which dies, and 

 sink to the bottom before ice formation sets 



^i<^. 



Fig. 9. — a. Hibernaculum ot Utrictilaria in October, h. Ter- 

 minal portion of stem in summer. c. Hibernaculum of Philo- 

 tria Canadensis (Elodea Canadensis), d. Terminal portion of 

 stem insttmmer: photographed in the air, 



in, and lie quiescent during the winter. After 

 the spring thaws, if one rows over the shal- 

 lows near a lake shore, he may see the hiber- 

 nacula resting on the bottom, and as soon as 

 the sun's rays have warmed the water suf- 

 ficiently to allow growth, a few rise to the 

 surface, and all begin to send out roots from 

 the lower end, and stems form at the upper 



