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 aqua- 

 tic seed plants are among the simplest of these devices. 

 Those of the common bladderwort are shown in figure 

 163. 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. 



