HABITS OF WEEDS 85 



up the struggle for existence. This habit of life makes it quite 

 easy to eradicate annual weeds by careful cultivation. If the 

 seeds are allowed to germinate and the young plants are cut 

 down before they flower, seed formation is prevented and the 

 plants have no other means of reproducing themselves. It is 

 necessary to keep a careful watch because some plants, such 

 as ivy-leaved speedwell, chickweed, shepherd's purse, pimpernel 

 and others begin to flower very early in life, and these early 

 flowers ripen and shed their seeds long before the latest 

 formed buds have opened. Many of the arable weeds are 

 annual in duration, some of the most common being groundsel, 

 spurry, poppy, chickweed, speedwells, pimpernel, charlock, 

 radish, thyme-leaved sandwort, fat hen, spurge, fumitory, and 

 cleavers, but the commoner weeds of grass-land usually live 

 longer, as the short-lived plants find it difficult to establish 

 their transitory existence under the conditions found in pasture 

 or meadow land. 



(2) Biennial Weeds. These are plants which spread their 

 life cycle over two years. In the first season the seed 

 germinates and vegetative growth is active, but flowers are 

 not produced. In many cases large quantities of reserve food 

 substances are laid up during this time and stored away in the 

 roots or underground stems for use during the following year. 

 In the second year the energies of the plant are directed to 

 seed formation, the reserves of food being used up for the 

 purpose of developing the flower and fruits. When this is 

 safely carried out the plant dies exhausted. 



If a biennial plant starts growing early in its first year, and 

 the summer is hot and dry, it often happens that flower forma- 

 tion is hastened. Under these circumstances, instead of wait- 

 ing till the second year, the flowering spikes are thrown up 

 and seed is produced at the end of the first season, so that 

 the weed becomes an annual for the occasion. The object of 

 this change of habit is, once again, to ensure seed formation, 

 for the biennials are as dependent as are the annuals on seed 

 for the propagation of their kind, not being provided with 

 means of vegetative reproduction. 



Very few weeds are truly biennial in habit, as they labour 

 under such serious disadvantages. The cultivation of the 

 soil during the growing season prevents the plants from mak- 

 ing much growth and from storing up food to tide them over 

 the winter. Even if they do escape for the time, it is more 

 than probable that spring cultivation will cut them up before 



