May6, i9i8 Yellow-Leafblotck of Alfalfa 327 



spores were found on diseased leaves of a plant in a protected location 

 which had grown more rapidly than most plants in the open field and 

 where infection must have occurred earlier. From this time on infec- 

 tion from overwintered material was reenforced with infection from 

 ascospores from diseased leaves of the current season's growth. 



During the summer, apothecia were found in great abundance in a 

 field left uncut for seed production. During the hot weather of July 

 and August these failed to open when soaked, and appeared to be entirely 

 lifeless. Yet, after the crop had been cut and the rains had come and 

 a new crop had sprung up, it was found to be very heavily infested with 

 the leaf blotch. In late October apothecia producing spores in great 

 abundance were found in these fields, and the late autumn growth 

 showed much of the disease. 



It is of interest to note that infected leaves which remain attached to 

 the plant appear to be much more favorably situated for the production 

 of apothecia than those which early fall on the ground. This is true both 

 in summer and in winter. Infected leaves which are early beaten to 

 the ground by rains rarely develop apothecia. The overwintered leaves 

 which produce apothecia most abundantly are those which have remained 

 attached to standing stems until early spring. 



Thus, it appears that apothecia readily survive the winter; possibly 

 others are developed from the stroma in the leaf in spring. The cold 

 weather of early spring appears to be unfavorable for abundant asco- 

 spore production; and the hot, dry weather of midsummer also has an 

 inhibiting effect. So far as observation has gone, ascospores appear to 

 be produced in sufficient amount to account for all infections that have 

 been observed. 



PENETRATION OF THE HOST 



In spite of considerable effort to determine the method by which the 

 germ tube from the germinating spores enters the leaf, only about a 

 dozen instances of penetration have been observed. Apparently, after 

 the germ tube has entered the leaf, the spore breaks away from the leaf 

 easily, and the relation of the mycelium to the exterior of the leaf is hard 

 to trace. But in the few instances which have been observed, the germ 

 tube has penetrated directly through the cuticle either immediately 

 beneath or close by the spore. In a majority of cases the spore has been 

 located at the junction of two epidermal cells, but in others the spore 

 was near the center of an epidermal cell. None of the germ tubes which 

 have grown out over the surface of the leaf have been seen to enter. 

 No case of entry through a stoma has been observed. 



METHOD OF DISTRIBUTION 



Up to the present the disease has been observed closely in but few 

 localities; in Wisconsin it has not been seen in newly seeded fields 

 which are several miles from old fields where the disease is known to 



