Natural grasslands, if undisturbed, possess a flora which has been built up during a long period of time, and which, like all purely natural plant associations, represents a delicate balance between its many constituents, which often include rare and shy species. If such land be once broken up, its flora will probably never again resume its former composition even if allowed to regenerate during a long series of years, for the alteration in the old substratum caused by its being turned over and mixed introduces new edaphic (_i.e._, soil) conditions which will not entirely pass away. As regards grazing, likewise, when land is pastured up to or near its full capacity, as is generally the case on enclosed areas, the weaker and often more interesting members of the flora tend to disappear. In primitive times all grasslands had, of course, their natural grazing inhabitants--in our islands deer of more than one species, sheep, and smaller creatures such as rabbits and geese--and so a total exclusion of grazing animals now would no more tend to reproduce exactly the flora of pre-husbandry days than does the excess of herbivores; but the present heavy stocking of the land is to be deplored by the botanist, even as it is rejoiced in by the economist. The more vigorous plants, and especially those which propagate themselves largely by vegetative means, survive, or even increase owing to the augmented food supplied by the manure which the animals provide; but many species fail to ripen seed, being either eaten or trampled; the rarer Orchids, strange ferns like the Adder’s Tongue (_Ophioglossum vulgatum_), and Moonwort (_Botrychium Lunaria_), and the other choicer denizens of the grasslands, tend to disappear. Drainage is an obvious cause of loss to our flora. Whole lakes and areas of swamp, with their peculiar and to a great extent natural flora, have disappeared from parts of the country. Some of the most interesting marsh plants of the British flora--such as the two fine Ragweeds, _Senecio palustris_ and _S. paludosus_, and the Marsh Sow-thistle (_Sonchus palustris_)--have on this account almost vanished from our islands, like the Bittern and Great Bustard which are their companions. Some lakes, again, have been ruined for the botanist by being used as reservoirs. The considerable changes of level which this involves is a thing to which plants are not adapted, and only a few can withstand it, such as the Water Bistort (_Polygonum amphibium_) and the Shore-weed (_Littorella uniflora_), which are equally at home on land or in water, being able to change rapidly their structure and mode of life to suit change of environment. As compared with a lakelet with a natural outlet, a dam with a sluice has always a much reduced and usually quite uninteresting flora.