56 BRITISH PLANTS 
on land, but which afterwards succeeded in making the 
water a place of abode. In the course of time they have 
become, by gradual modification, better adapted to a 
watery existence, but traces of their terrestrial origin 
always remain. The oldest aquatics are, naturally, most 
changed (Lemna, Elodea, Ceratophyllum), while the latest 
emigrants from the land differ little in organization from 
ordinary land-plants—e.g., water-buttercup and water- 
violet. Thus, when we find an aquatic whose vascular 
tissue has lost all trace of lignification (e.g., Ceratophyllum), 
which has no stomata or no roots (bladderwort), we know 
that we are dealing with a very ancient race which has 
lost most of its land-characters through its long sojourn in 
the water. Probably the oldest aquatics are the duck- 
weeds (Lemna), which seem to have lost all the characters 
of land-plants except their method of flowering. Of all 
organs the flower is the most conservative, and, except in 
a few cases, all water-plants still send their flowering shoots 
into the air, where the flowers are pollinated by the 
same means as their relatives on land. Some aquatics, 
indeed, possess large and quite showy flowers—e.g., 
water-lobelia, water-violet, bladderwort—all of which are 
pollinated by insects. 
Some of the very recent inhabitants of the water 
live equally well on land—e.g., Polygonum amphibium. 
These are amphibious plants (p. 28), and it is from 
among the amphibious plants which throng the edges of 
water everywhere that the aquatic vegetation is con- 
tinually being recruited. 
