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Pomona College Journal of Economic Botany. 



are formed by being cut off from the ends of liyphal l)ranclies. Sometimes 

 a spore is cut off from the end of a terminal branch, but more commonly 

 from the ends of short lateral branches l)y a constriction furrow. As soon 

 as one macroconidium is cut off, the hypha bcfrjns to elongate, pushing 

 past it and soon forming a second constriction furrow, which cuts off a 

 second macroconidium. This process continues until sometimes eight or ten 

 macroconidia are formed from a single branch and lie side by side in a 

 little group. Sometimes the septa are formed in the macroconidia before 

 they are cut off l)ut more frequently afterwards (Plate V Figures 1 

 2, and 3). ' ' 



The exact time required for the formation of the macroconidia ha.s 

 not been determined, but the process must be very rapid, for hundreds 

 will develop in a single spore drop within two or three days after they 

 have started to form. The macroconidia vary in length from 25 u.-60 u. 

 and in width from 4 u.-f) u. When these conidia are first formed they 

 are cylindrical in shape, rounded at the ends and nearly straight. With 

 age they l)ecome much more pointed at the ends and more curved. They 

 are from one to six septate, usually three or four; they are seldom con- 

 stricted at tlie septa. ^Macroconidia formed upon the plant in the open are 



y PLATE V 



