LAKES AND TARNS 141 



which a member of a thoroughly terrestrial family 

 becomes accustomed to life in water. The flowers 

 have a delicate lilac colour and are raised on slender, 

 tremulous stalks ; when hundreds are seen together as 

 we saw them that August day the water seems to be 

 enchanted. 



When plants growing in the water lift their flower- 

 heads high, the pollination is effected by insect visitors. 

 We know, for instance, that the golden-yellow flowers 

 of the Bladderwort are visited by long-tongued 

 Syrphid Flies, which carry the fertilising dust from 

 blossom to blossom. In the case of the submerged 

 flowers of some of the Pondweeds the pollen may be 

 carried by gentle currents in the water. But there is 

 a good deal to be found out yet in regard to the 

 pollination of aquatic plants. 



Compared with terrestrial plants, those that live in 

 water tend to be rather degenerate. They have gone 

 back in evolution, and yet the retrogressions may be 

 well suited for aquatic life. In his great work, " The 

 (Ecology of Plants " (1909), Professor Warming 

 notices the following adaptations among others : 

 (i) Since the whole surface may absorb water and 

 dissolved salts, the roots may be absent, or degenerate, 

 or arrested. (2) Water-carrying tubes are less in 

 demand than in land plants, and therefore but slightly 

 developed. (3) Supporting tissue, such as wood, is 

 reduced or undeveloped because the plants are buoyed 

 up by the water. (4) Air-containing spaces are very 

 abundant and help not only for flotation, but as aids 

 in gaseous interchange. (5) The skin of the sub- 

 merged parts is very thin and often green. (6) 

 Transpiration having ceased from submerged parts, 



