1915] 



OVERHOLTS STUDIES IN THE POLYPORACEAE 673 



Falck 1 showed that the mature spores of certain species of 

 Lenzites were very constant in the length of their short axes, 

 the variations being only a fraction of one micron, while the 

 length of the long axis varied considerably, although in that 

 case the variation rarely went beyond 3 ju in different spores 

 from different fruit bodies. Cotton 2 investigated variations 

 in the spores of Stropharia semiglobata and found that when 

 the pileus was cut from the stem and a series of spore prints 

 obtained from the former, the spores shed during the first 

 hour measured 18 X 10 n, while those shed during the twenty- 

 third hour measured 15 X 9 n, and those shed during the 

 eighty-third hour measured only 12 X 7 /i. The diminution in 

 size was ascribed to the artificial conditions, i. e., the pileus be- 

 ing severed from the stipe, under which the spores were pro- 

 duced. Experiments carried on with sporophores collected 

 and placed in large test-tubes and supplied with water, showed 

 that the spores shed the first day did not differ in size from 

 those shed during the fifth or sixth day. The first experiment 

 suggests the possibility that in plants growing in nature the 

 size of the spores might be reduced if the fungus was grow- 

 ing on a substratum in which the required amount of food 

 substances was not present. No comparative studies along 

 this line have yet been reported and the question of the 

 amount of variation in size of spores is still an open one. 

 However, spore measurements have been very successfully 

 used in separating species of fungi and no doubt the limit of 

 their usefulness has not yet been reached in systematic 



mycology. 



Inaccurate spore measurements may creep into the litera- 

 ture through a misdetermination of species quite as easily as 

 species may be misdetermined because of inaccurate spore 

 measurements. The former condition is especially liable to 

 be pronounced in the literature of a fungous flora as little 

 known as is that of this country, and where species are not 

 determined on microscopic characters, but these same char- 

 acters are entered in the literature when the species is re- 



1 Moeller's Hausschwamm-forschungen, Heft 3, pp. 79-90. 1909. 



3 



Trans. Brit. Myc. Soc. 4: 298-300. 1914. 



