120 THE NATUEE AND WORK OF PLANTS 



identity with the kinds seen the previous autumn. 

 They are plentifully furnished with red and purple 

 coloring inatter as a result of the low temperatures 

 under which they have lived. 



166. Behavior of the hibernacula. The hiber- 

 nacula sink to the bottom of the water in the 

 autumn, and thus escape the action of the ice. This 

 is also done by the minute pond-scums and other 

 forms which are seen to float on the surface in great 

 quantity in the summer. When the ice disappears 

 in the spring and the sun's rays begin to warm the 

 water, several bubbles of gas are formed in them, 

 which helps float them to the surface. Now the 

 bud begins to unfold, and the tip of the enclosed 

 stem to grow in length, while long roots grow out 

 from the basal end. Perhaps it finds lodgment in 

 the mud in shallow water, and the new season's work 

 is begun. 



All water plants do not form such buds. Water 

 lilies have great stems lying imbedded in the mud at 

 the bottom of the pond, and these send up leaf and 

 flower stalks which reach the surface and perform 

 their function during the summer, dying down on 

 the approach of cold weather. 



