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NEW JERSEY AGRICULTFEAL COLLEGE 



mildew of the grape, another of indoor lettvice, another of onions, 

 while the potato-rot fnngus, often extremely destructive, is very near 

 of kin to the bean PJijjtophthora. Figure 5 gives some of the micro- 

 scopic details of the mildew. At a is shown a portion of the diseased 

 bean pod witli the threads passing through the stoma and bearing the 

 spores upon tlieir tips. A more enlarged view of the mildew is shown 



at b. The enemy in question 

 belongs to a group of fungi the 

 members of which are among 

 the most fatal of all that afflict 

 crop plants, and therefore de- 

 mand prompt attention upon 

 the part of the grower when 

 met with. 



Precautions. — Some hints as 

 to precautionary measures may 

 l)e gained by a knowledge of 

 the habits of the group to 

 which the mildew of the lima 

 beans l)elongs. After a some- 

 what prolonged study of the 

 relation obtaining between the 

 weather and the development 

 of fungi, it may be confidently 

 asserted that there is no group 

 that is more influenced by pre- 

 vailing moisture than the 

 downy mildews. The potato- 

 rot fungus (Phytophtliora in- 

 festans DeBy.) is particularly 

 fond of wet weather, with high 

 temperature, and the records 

 show that 1899, the year wdien the bean Phytophtliora was discovered, 

 was remarkable for its excessive summer and autumn rains. In the 

 case of greenhouse lettuce it is found that sub-irrigation is almost a 

 complete preventive of the mildew, otherwise often quite destructive. 

 It is safe to assume, therefore, that the amount of the bean mildew will 

 depend quite largely upon the amount of moisture, and, in a dry sea- 

 son, but little damage may be expected from it. But the rains cannot 



Pig. 5. 



Microscopic Details of the Mildew. 



