A Study of Meadow-Crop Diseases in New York 39 



the fungus tends to cease sporulating. By allowing a pure culture to 

 discharge spores onto plants under a bell jar copious infections have 

 resulted repeatedly on red and alsike clovers, and once a few minute spots 

 showed on white clover. Reisolations were successful from the red and 

 alsike clovers, giving a fungus indistinguishable from the original culture. 

 No reisolation was attempted from the white clover. The results of these 

 inoculation studies agree with those of Jones (1919:22), who inoculated 

 red and alsike clover successfully but who did not use white clover. 



Frequently infections are so plentiful on red and alsike clover that the 

 leaves appear peppered with small brown spots, as shown in figure 7. 

 Under such conditions apothecia are not developed. 



Life history. Overwintered living leaves in the spring bear apothecia 

 that discharge their ascospores to initiate the primary infections. Apo- 

 thecia have been known to shoot their spores at least 5 millimeters directly 

 upward to agar in inverted petri dishes. According to the work of Buller 

 (1909), air currents are capable of wafting spores from such a height to 

 the lower leaves. No satisfactory explanation of the distribution from 

 one country to another can be offered as yet. There is no good evidence 

 that the fungus is seed borne. 



Jones (1919) has made a careful study of the phenomena of incubation 

 and infection of this fungus in red clover. Germination in the laboratory 

 is not more than 50 per cent, as a rule, even when spores are discharged 

 on plain agar, the best medium for the process. A tube is sent out within 

 twelve hours from any point on the circumference of the spore and passes 

 directly through the cuticle into the leaf. Epidermal and palisade cells 

 resist disintegration until hyphae become very numerous. Germ tubes 

 may enter uncongenial suscepts such as yellow trefoil but cause only a 

 slight yellowing before the germ tubes die. Red- and alsike-clover leaves 

 inoculated at Ithaca in the greenhouse showed very minute brown spots 

 within four days. These enlarged up to 1 millimeter within a fortnight, 

 at which time severely infected leaves were dead. 



The secondary cycles follow each other at about three-weeks intervals. 



Epiphytology 



The disease seems to be favored by wet weather. For example, a thick 

 stand of clover in a field near Kingston, New York, situated in a creek 

 bottom on good soil, was very severely affected in June, 1928. The 

 grower attributed the unusual dying of the lower leaves on his plants to 

 the very wet spring, but an examination showed that P. trifolii was attack- 

 ing the leaves heavily. The spots, which were the largest that the writer 

 had ever seen, contained large amber apothecia that were discharging their 

 ascospores in abundance. Undoubtedly this disease played the chief role 

 in killing the leaves. Water is highly essential for the discharge of the 

 ascospores and for their dissemination. 



