288 Riley : Plowrightia morbosa Spores 



thorough examination as late as May 9 showed that fully three 

 fourths of the spores were immature. 



The possibility of exceptional exposure of the knots examined 

 is precluded by the fact that I had under observation a number of 

 trees, growing in diverse situations. It occurred to me that the 

 winter might have been an unusually severe one. On this point, 

 fortunately, the records of the weather station, located here, 

 furnish reliable data. Until January, the winter was mild. Con- 

 sidering as normal the mean temperature for twenty years, the 

 average for the months of January and February, 1899, was two 

 and seven tenths degrees below the normal. On the other hand, 

 the mean temperature for March was slightly above while that for 

 April w T as four and two tenths degrees above normal. Moreover, 

 11 It's a poor rule which will not work both ways"; the present 

 winter has been an unusually mild one. The mean temperature 

 for January was three degrees above the normal. So far, the 

 temperature this month has been unusually mild. Yet, up to the 

 present (Feb. 17), I have found no fully outlined spores. That 

 exceptional weather may affect the maturation of the spores is un- 

 doubted. It is, however, evident that, for this locality, the asco- 

 spores of Plowrightia morbosa normally mature considerably later 

 than the time recorded by Dr. Farlow and others. 



I find that a similar instance of slow development in the vicinity 

 of Ann Arbor has been reported by A. A. Crozier.* 



Botanical Department, Cornell University. 



* Botanical Gazette, 10 : 368. 1885. 



