Variations in the Maturing of Plowrightia morbosa Spores 



By Wm. A. Riley 



During the course of some work upon the black knot fungus, 

 I was interested in noting the time of maturing of its ascospores, 

 in the neighborhood of Ithaca. Between the actual date for this 

 locality and the time which has been recorded for the New Eng- 

 land and Middle States there is a decided discrepancy. 



The first statements bearing upon this are those of Prof. C. H. 

 Peck.* He notes that, "in specimens collected January 13th, 

 spores were found in a few of the sacs but most of them were yet 

 filled with their greenish contents/' He states that he found 

 spores as late as June. 



Dr. W. G. Farlowf first found a few ripe spores on the 17th 

 of January, and in the second week of February, most of the knots 

 examined contained ripe spores. He found that late in the spring 

 they were not so abundant or in such good condition. Dr. Hum- 

 phrey, X who studied the fungus in the vicinity of Amherst, con- 

 firms Dr. Farlow's dates. 



My observations commenced early in February of last year. 

 On the 1 2th of that month I examined a large number of speci- 

 mens and failed to find a trace of spores. My interest being 

 aroused, I made throughout the term, two or more observations 

 per week, usually examining a large number of knots from several 

 different trees. 



Not until March 7, after a week of mild weather, did I find a 

 single ascus containing fully formed spores. March 22 specimens 

 found on young shoots, where they had been protected and kept 

 moist by snow, showed in the majority of the asci fully formed 

 spores. Knots taken from the branches of the same tree showed 

 that in most of the asci the spores were, at best, but faintly out- 

 lined. In only a very few asci were they nearly mature. By the 

 middle of April the mature spores were fairly abundant but a 



Trans. Albany Inst. 7 : 199. 1 87 2. 

 fBull. Bussey Inst., 442. 1876. 

 J Rep. Mass. Agr. Exp. Sta. 8 : 206. 1 890. 



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