60 BRITISH PLANTS 
the physiological winter—e.g., Cerastium semidecandrum, 
Trifolium arvense, Aira precox, Bromus mollis, Phlewm 
arenarium, Jasione montana, and Draba verna (see p. 107). 
(6) Weeds of Cultivation in dry fields and waste places 
—e.g., cudweed (woolly), Lepidium ruderale (leaves small, 
plant shrubby), corn-spurrey (fleshy), Sawifraga tridactyl- 
ites (rosette-form), etc. 
3. Mesophytic Annuals—e.g., corn-buttercup, corn- 
cockle, herb-Robert, black medick, fool’s-parsley, cleavers 
(a climber), yellow rattle, Poa annua, ete. 
Biennials.—Most biennials at the end of the first season 
die down to tuberous underground structures (p. 111). 
These often carry a rosette of radical leaves close to the 
ground (see rosette-type, p. 37)—e.g., foxglove, carrot, 
burdock, ox-tongue, etc. 
Deciduous Trees and Shrubs.—At the approach of winter, 
these plants lose their leaves. They are not destroyed by 
cold or stripped off by the wind, but are discarded, as it 
were, by an act of the tree itself. The deciduous leaf is 
essentially a summer leaf, typically large, thin, hori- 
zontally placed, exposed freely to the light and the wind, 
and richly provided with stomata on its under surface. 
Although these characters favour transpiration, there is 
little danger of excessive transpiration in summer, because 
the soil is warm and the supply of water is adequate. In 
winter, however, the possession of these leaves would be 
injurious, and in most cases fatal to the plant. The soil 
is cold, and very little water is absorbed by the roots. 
If, under these circumstances, transpiration could not be 
controlled, the plant would lose more water than it could 
get, and death would follow from drought. To meet this 
peril, the tree forms a layer of cork across the base of the 
leaves in autumn. The leaves, thus cut off from their 
water-supplies, dry up and die, and, a layer of cells just 
outside the cork splitting, they easily become detached 
and fall to the ground. And so the tree, which during 
the summer stood up, with its thousands of expanded 
leaves—a typical mesophyte— becomes now a leafless 
xerophyte, with bare cork-covered twigs, and the buds 
which will renew its foliage in the spring protected from 
desiccation in many and wonderful ways. 
Buds and Bud-Protection.—In perennial plants, the 
assimilating organs are formed in buds, which are situated 
