4 INTRODUCTORY 



The succession of events is generally in this order, and usually 

 the formation and unfolding of roots, stems, and leaves occupies 

 by far the greatest portion of the plant's life. 



There is, however, great variation in the time taken to 

 reach the several stages of development, and the periods 

 are not always of the same duration in the same species of 

 plant, 



4. So far as their total duration of life is concerned, plants 

 may be usefully divided into annuals, biennials, and peren- 

 nials. 



By an annual is meant a plant which completes its life-history 

 in one growing season. Starting as a seed in spring or early 

 summer, it develops root, stem, and leaves, and then produces 

 flowers and seeds, after which it dies, leaving behind it offspring 

 in the form of seeds. The time taken by annuals to reach the 

 stage of seed-production is not always the same ; usually the 

 whole of the season, from spring to autumn, is necessary, and 

 only one generation is produced in that time. Some of them, 

 however, termed ephemerals, such as chickweed and groundsel, 

 produce seeds in a few weeks, and these may germinate and pro- 

 duce a second and third crop of plants before frost cuts them 

 down in autumn and winter. 



Biennials, beginning life as seedlings in spring or summer, 

 occupy the first growing season in the production of root, stem, 

 and leaves only. They then rest during winter, and in the 

 following year start growth again, and produce a stem bearing 

 flowers and seeds, after the ripening of which the plant dies. 

 Wild carrot, parsnip, and some varieties of thistles behave in this 

 manner. 



Perennials are plants which live more than two years, and 

 often several seasons elapse before flowers and seeds are produced. 

 They are frequently divided into two classes, namely, (i) herbaceous 

 perennials and (2) woody perennials. In the former the leaves 

 and stems above ground are of a soft nature and die down at the 



