WEEDS 175 



in California. It differs from most other weeds in 

 giving the farmer no rest in summer. Starting in early 

 spring, it matures seeds in May. These germinate 

 when it is so dry that scarcely anything else will grow ; 



FIG. 91. Sheep Sorrel. (About natural size.) 



and soon produce another crop of seed. This second 

 crop of seed may also grow and produce seed in De- 

 cember. 



In pastures it is even worse than in cultivated fields, 

 for it soon kills out the grass and takes complete pos- 

 session of the land. It perfectly illustrates the survival 

 of the fittest. 



Wild mustard and radish. The black mustard and 

 yellow mustard (also called white mustard and yellow 

 turnip), with their masses of yellow flowers, are very 

 well-known weeds. In the seedling stage, as shown in 



