140 PLANTS AND MAN 
for the alteration in the old substratum caused by its 
being turned over and mixed introduces new edaphic 
(z.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 them- 
selves 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 (Botry- 
chium 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 inter- 
esting marsh plants of the British flora—such as the 
two fine Ragweeds, Senecio palustris and S. palu- 
dosus, and the Marsh Sow-thistle (Sonchus palustris) 
—have on this account almost vanished from our 
