FRIENDS AND ENEMIES OF PLANTS 175 



1. Their numbers will increase from year to year, and much 

 labor will be required to eradicate them. 



2. They appropriate the nourishment of the soil and diminish 

 the supply needed by our cultivated plants. 



3. As they make a rapid growth they shade the ground 

 and may shut out warmth and sunlight much needed by the 

 plant. 



4. When abundant they shut off the ventilation and soon 

 smother out the smaller plants. 



5. They rapidly deplete the supply of moisture in the soil, 

 which should be reserved for the cultivated crop. 



Canada thistle. Sow thistle. 



6. It is thought that many diseases of both plants and animals 

 are caused by the presence of luxuriant growths of certain obnox- 

 ious weeds. 



7. Weeds are frequently injurious and even poisonous to 

 stock. Both cattle and horses are frequently killed by eating 

 the loco weed, while every one is familiar with the fact that wild 



