108 BRITISH PLANTS 
Gardeners obtain early spring flowers by sowing hardy 
annuals at the endof summer. These germinate in the 
autumn and bloom early in the spring, and the flowers then 
last longer than usual—e.g., cornflower, poppy, sweet pea. 
The fecundity of some annuals is so great and the lives 
of the individuals so short that several generations are 
produced in the course of the year—e.g., Poa annua, 
sroundsel, chickweed, shepherd’s-purse. 
Annuals are characteristic of temperate regions, where 
there is a marked alternation of seasons, and the summer 
is sufficiently long to allow the plants to proceed from 
seed to seed again. The seed, in which the young plantlet 
hibernates, is a pronounced xerophytic structure, and can 
withstand the most extreme and prolonged hardships 
(see p. 74). The great majority of the so-called weeds of 
cultivation are annuals, as naturally they must be, for they 
are destroyed regularly at harvest-time, and their propaga- 
tion is dependent entirely upon the seed left behind in the 
ground after the crop and its weeds have been removed. 
There are very few annuals among alpines and aquatics. 
2. Biennials——These plants, as the name implies, live 
during two vegetative seasons. During the first they 
produce leaves and manufacture food, which is stored up 
in their underground parts for use the next season, when 
they flower, seed, and die—e.g., turnip, carrot, foxglove, 
burdock, mullein. The swollen underground organs 
found in biennials at the end of the first season are merely 
temporary reservoirs of food. During the formation of 
the seed, a steady migration of food-material takes place 
from these organs, which become depleted, and ultimately 
shrivel up. Essentially, biennials differ little from 
annuals, and especially from those which we have called 
autumn-annuals. They only seed once, and under un- 
favourable conditions they may even flower the first year 
and die, while in a few cases strong and vigorous plants, 
enjoying the advantages of a good soil and a happy 
habitat, may live for several years. The latter is fre- 
quently the case with wild biennials grown in gardens— 
e.g., wallflower, foxglove. 
3. Perennials.—Perennials are plants which live for 
more than one year, and seed several times before they 
die. All parts of a perennial have not the same longevity ; 
some parts live longer than others. The leaves of a 
