46 PLANT ASSOCIATIONS 
Duckweeds (Wolffiia arrhiza) and the Bladderworts 
(Utricularia), have gone farther still, and have dis- 
pensed with roots altogether. In Wolffia, indeed, the 
degeneracy of structure which results from the 
simplification of life problems in plants which live 
thus floating freely in water, is carried to its extreme 
limit. Leafless, rootless, and almost flowerless, it 
maintains itself by the budding of its tiny green 
fronds, a life-history as primitive as that of the lowly 
Algz among which it lives. In the Bladderworts, the 
long flaccid stems, clothed with much-divided leaves 
converted in part into ingenious imnsect-traps (see 
p. 188), hang limply in the water, sending up boldly into 
the air their flowering shoots with yellow Snapdragon- 
like blossoms. In most of such free-floating plants, 
compact buds are formed at the tips of the shoots 
in autumn, and while the rest of the stem dies away 
these sink to the bottom and remain there safe from 
frost and storm until the spring, when they rise to the 
surface and produce a new crop of plants. 
We have now glanced at the most distinctive of the 
plant formations which we meet with in our own 
country, and find that they accompany extreme con- 
ditions relating to water and soil: it remains to return 
to the consideration of the vegetation which de- 
velops under conditions of a more normal character— 
on ordinary soils, in fact, which are neither very wet 
nor very dry. Such conditions are precisely those 
which are required for agricultural purposes; and - 
over the wide areas where they prevail, we find, as 
pointed out already, mere fragments of the native 
associations remaining in an undisturbed condition. 
This renders their study more difficult, and the diff- 
