ADJUSTMENT OP ORGANISMS TO ENVIRONMENT 375 



from those in deep water, except at depths they themselves 

 cannot endure. Adjustments in time are indicated in the 

 last column of the preceding table for the single season. 



FIG. 218. A damselfly (Lestes uncatus). 



These are mutual adjustments and involve succession of 

 periods of vegetative activity. Time adjustments that 

 extend over long periods, and that accompany slow changes 



