CHAPTER V. 



HABITS OF WEEDS. 



THE habits of growth and the length of time that weeds live 

 have much to do with the methods adopted in dealing with 

 them, and also with the amount of damage that they are able 

 to inflict upon crops. A knowledge of the way in which a 

 particular weed grows is often a valuable asset to the farmer, 

 enabling him to eradicate it in the most effective way, and in 

 some cases an understanding of the life history of a plant 

 reveals some weak point in development at which it may most 

 readily be attacked with every hope of success.. 



Duration of Weeds. Weeds may be divided into three 

 classes according to the length of time they live : 



(i) Annual Weeds. These are plants in which the whole 

 cycle of existence is completed within twelve months. After 

 germination the vegetative growth is rapid, so that the plant 

 is in flower within a comparatively short space of time. 

 The ripening of the fruits is equally rapid, and the pro- 

 duction of seed is thus ensured. Annual weeds depend 

 entirely upon seed for their reproduction, and the whole 

 energies of the plants are directed towards the formation of 

 this essential. As a general rule the quantity of seed produced 

 is very abundant, so that even though much of it may be lost 

 by decay or other means a sufficiency is left to carry on the 

 species. If the season be hot and dry, and there is danger that 

 plant life will suffer from drought, the annual weeds hurry into 

 flower at an early stage of development in order that they 

 may not die before their seeds are formed. It is no uncommon 

 sight in a dry summer to see the most miserable specimens 

 putting up a weak flower and then ripening miniature seed 

 pods. The same effect is produced by other adverse circum- 

 stances, such as the presence of poisonous substances in the 

 soil. Unless they are killed outright, annuals strive to the 

 very utmost to produce some stock of seed before they give 



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