410 RESEARCHES ON FUNGI 



but, in actual fruit-bodies, the colour of the spores is not in the 

 least dependent on the number of spores produced per basidium, 

 but only on the degree of spore-maturity. 



In a variety of Cultivated Mushroom, which I grew on a bed 

 of horse manure at Birmingham, England, the basidia were found 

 to be usually bisporous ; but, mixed with the bisporous basidia, 

 were a larger or smaller number of monosporous basidia. An 

 area of the hymenium showing spores in pairs (represented in 

 uniform black) and single spores (shaded with lines) is illustrated in 

 Fig. 143, C. Bisporous basidia, as well as a few monosporous 

 basidia, are also shown in Fig. 142 (p. 407). 



In no fruit-body of the Wild Mushroom could I find a basidium 

 with either one or two spores upon it ; and, corresponding with 

 this, in no fruit-body of the Cultivated Mushroom could I find a 

 basidium with either three or four spores on it. However, it would 

 not be a matter of surprise to me if varieties of Mushrooms were 

 discovered in which monosporous, bisporous, trisporous, and 

 quadrisporous basidia occurred mixed together on the same 

 hymenium. 



It was pointed out in the first volume of this work that both 

 Atkinson and I have found two-spored varieties of Mushrooms 

 coming up upon the campus of our respective Universities. 1 It 

 is therefore possible that, in North America at least, there is a 

 Wild Mushroom with two-spored basidia ; but, to obtain certainty 

 in this matter, further observations are necessary. It seems very 

 likely that the two-spored varieties of Psattiota campestris have 

 been derived by mutation from the four-spored. 2 



In regard to the size of the spores, it is to be noted that the 

 spores on a trisporous basidium in a Wild Mushroom are slightly 

 larger than those on a quadrisporous basidium (Fig. 143, A and B, 

 p. 409), and also that the spore on a monosporous basidium in 

 a Cultivated Mushroom is distinctly larger than the spores on a 

 bisporous basidium (Fig. 143, C). In giving the average size of 

 the spores, this fact ought to be taken into account. Usually, in 

 a spore-deposit from a Cultivated Mushroom, one can distinguish 

 by their size with a fair amount of certainty which spores have 

 1 Vol. i, 1909, p. 15. 2 Ibid. 



