FUNGI IMPERFECTI 



311 



as in a moist" chamber, the length mentioned may be considerably 

 exceeded. After the death of a leaf, spores may be produced over 

 the entire surface. Spores found upon old leaves in the field five 

 months after the beets were harvested were able to germinate. 



The fresh spores germinate readily in ordinary nutrient media, 

 and pure cultures may be obtained by the poured plate method. 

 After a growth of a few days the colonies show up well. The sub- 

 merged mycelium develops in agar as a dense olivaceous colony, 

 the new growth lighter in appearance, forming an outer border. 

 The aerial growth of the colonies is finally grayish green. On 

 bean pods a copious development of mycelium occurs, but such 

 cultures maintained 

 for two years gave 

 no production of 

 conidia. Abnormal 

 conidia may, how- 

 ever, be developed 

 on this medium 

 from other species 

 of Cercospora in cul- 

 ture. Aerial hyphae 

 show a tendency to 

 adhere together in 

 slight strands or 

 clusters, and the 

 small branches sug- 

 gest an attempt at spore production (Fig. 144, aerial). The im- 

 mersed mycelium is very irregular, with many swollen cells and 

 peculiar branches (Fig. 144). I have grown about twenty spe- 

 cies of Cercospora in pure cultures, but in no case has any evi- 

 dence or clue been obtained as to the possible connection with 

 a perithecial form. 



Control. Such experiments as have been made indicate that 

 this disease can be controlled, where necessary, by Bordeaux 

 mixture. Since the conidia may retain their vitality until late 

 winter, it is probable that many are able to germinate after the 

 seed are sown in the late spring; early spraying is therefore 

 important. 



Fig. 144. 



Mycelium of Cercospora in Culture: 

 Aerial and Submerged Forms 



