FUNGI IMPERFECT! 



359 



The Kieffer is practically exempt. In any case, however, the 

 fungus may be readily controlled with Bordeaux. 



The spots on the leaves are few or numerous, angular, and the 

 size varies greatly with the variety. Three fairly well differentiated 

 zones of color are shown in an affected spot : at the center it is 

 ashen gray, and within this area appear on either surface the minute 

 pycnidia ; the next outer zone, or area, is brown, or black in very 

 young leaves ; and surrounding this second there may be an area 



Fig. 177. Dilution Culture of Septoria Pyricola 



which is purplish in color (Fig. 176). These color details are lost 

 in very old leaves, but the black papillae indicating the pycnidia 

 then show up clearly. At maturity the spores may ooze out in dark 

 uniform cirras. In cross section the pycnidium is clearly ovate in 

 form. The wall is made up of several layers of dark cells, and the 

 hyaline conidiophores arise from an inconspicuous inner layer 

 (Fig. 178). The spores are flexuous and quite constantly two- 

 septate, measuring about 60 x 3-4 /x. The mycelium is intercel- 

 lular, brownish, and may be detected within the tissues at some little 

 distance from the perithecium. The spores germinate readily in 



