STEMS 125 



The number of individuals which attempt to grow 

 on any given spot, however, is many times greater 

 than it can support. The species which are capable 

 of sending up long stems quickly will reach the 

 sunlight and live while their slower and weaker 

 neighbors will be choked or shaded out. In this 

 fight the stem is the chief weapon. 



173. Weeds. — In the cultivation of crop plants 

 all species are killed by the farmer except the one 

 desired, thus removing it from the struggle for 

 existence with neighbors. Certain forms, however, 

 have habits of growth which adapt them for gaining 

 a foothold among the cultivated forms, and this 

 makes them weeds. Before the country was settled 

 or cultivated there were no weeds, of course. Vigor- 

 ous and rapid growth of the stems is the principal 

 characteristic of weeds. The stems do not alwaj^s 

 stand erect, but may carpet the soil and hinder the 

 growth of other plants in this manner. Find and 

 describe the habits of three weeds. 



174. Climbing stems. — In the struggle to get 

 the leaves and flowers up to the sunlight, a number 

 of species have formed the habit of clinging to the 

 stems of other plants. This is done by two methods : 



