264 Adjustment to Conditions of Aquatic Life 



Unlike other parts of the plant, its specific gravity is 

 greater than that of water. It is enveloped only by a 

 thin gelatinous covering. With its development the 

 functional activity of the old plant ceases; the leaves 

 lose chlorophyl; their bladders fall away; the tissues 



Fig. 164. The remains of a fresh- water sponge that has 

 grown upon a spray of water-weed. The numerous 

 rounded seed-Hke bodies embedded in the disintegrating 

 tissue are statoblasts. See text. 



disintegrate; and finally the hibernacula fall to the 

 bottom to pass the winter at rest. When the water 

 begins to be warmer in spring, the buds resume growth, 

 the axis lengthens, the leaves expand, air spaces 

 develop and gases fill them, buoying the young shoots 

 up into better liglit, and the activities of another season 

 are begun. 



