Encystment 



263 



body. It forms this cocoon about the latter end of 

 May. It reposes quietly upon the bottom during the 

 entire summer — thro a longer period, indeed, than 

 that of absence of oxygen from the water. Hatch- 

 ing and resumption of activity begin in September and 

 continue into October. Marsh (09) suggests that 

 with us this species "may be considered preeminently a 



Fig. 163. Hibernacula of the common bladderwort. 



winter form." It is active in summer only in cold 

 mountain lakes. 



The over-wintering buds (hibernacula) of some aquat- 

 ic seed plants are among the simplest of these devices. 

 Those of the common bladderwort are shown in figure 

 1 63 . At the approach of cold weather the bladderwort 

 ceases to unfold new leaves, but develops at the tip of 

 each branch a dense bud composed of close-laid incom- 

 pletely developed leaves. This is the hibernaculum. 

 It is really an abbreviated and undeveloped branch. 



