108 BRITISH PLANTS 



Gardeners obtain early spring flowers by sowing hardy 

 annuals at the end of 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, 

 groundsel, 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.gr., 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 



