HARMFUL WEEDS 105 



Weeds grow where other plants cannot live. Many weeds, 

 because of long roots and small leaf surface, are fitted to live where 

 there is little water supply, or even in drought or desert condi- 

 tions. Such are the Russian thistle, some of the true thistles, 

 the poisonous loco weed, and our common ragweed. Many, at 

 least when young, can get along in the shade of competing plants, 

 their rapid growth enabling them to get into the sunlight later on. 

 Such are the mustards which often color entire fields yellow with 

 their tiny four-petaled flowers. Still other weeds seem to thrive 

 under conditions of soil not suitable for other plants. Such are 

 some of our desert and alkali-loving plants. 



Self-Testing Exercise 



Weeds are plants that (1) where they are not (2). 



They are usually (3) and (4) faster than agricultural 



plants. They rob crops of (5), (6), and (7). 



Weeds produce many (8). Weeds are plentiful because 



they have good methods of (9) (10), have great 



(11) and (12) where other plants cannot. 



PROBLEM II. WHY AND HOW SHOULD WEEDS BE 

 ERADICATED? 



Harmful weeds. Weeds do harm in a number of ways. They 

 reduce the farmer's crops tremendously. We have already seen 

 that they force slower growing plants out. Think of the amount 

 of productive labor lost through keeping weeds out of gardens and 

 fields. Weeds are often introduced into fields through the mixing 

 of their seeds with those of grains, or other crops bought for plant- 

 ing. We can learn to identify such seeds under the microscope, 

 and some farmers have such a test made to see if the seed they 

 buy is pure. Weeds take the minerals and water from the soil 

 much faster than the competing crops because they grow so 

 quickly. Poisonous weeds, such as the loco weed, may kill or 

 injure cattle. Some parasitic weeds like dodder, in the far West, 

 kill great numbers of other plants. Another weed, the tall bar- 

 berry, harbors another much more dangerous parasite, the wheat 

 rust. Some wild grasses are inhabited by the pupae of the Hes- 



