Plants as Affected by Weeds. 187 



(332)). To this class belong the powdery mildews of 

 the grape,* apple,! etc. 



335. The Cultivator will often Need to Consult the 

 Specialist in dealing with fungous diseases. In many 

 cases, it will be difficult or impossible for him to decide 

 as to the exact nature of a given trouble without train- 

 ing and skill in the us.e of the compound microscope. 

 Specialists in this line are now employed by the govern- 

 ments of most civilized nations and by many agricul- 

 tural experiment stations, and they should be freely 

 consulted. Much may be learned, however, by studying 

 the best books on the subject. The cultivator should 

 be able to recognize the principal fungous diseases. 



Section VIII. Plants as Aj^fected by Weeds. 



336. Weeds are plants of the higher orders that per- 

 sist in growing where they are not wanted. They in- 

 jure the desirable plants about which they grow by 

 robbing 'them of light, moisture and food, and their 

 presence is an evidence of slovenly culture. The re- 

 markable vigor and prolificacy possessed by many weeds 

 would enable them to soon overcome most cultivated 

 plants, but for the aid of the cultivator. As with 

 harmful insects and fungi, prompt and persistent ef- 

 forts are essential to the control of weeds in most cul- 

 tivated grounds. 



337. Annual, Biennial and Perennial Weeds. With 

 reference to their term of life, weeds and other plants 

 are divisible into three classes, viz., annual, those that 

 live but one season; biennial, those that live only two 



* UnciiMila necator. t Podosphaera oxycanthae. 



