36o 



RESEARCHES ON FUNGI 



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angle of about 25°, the third descends at an angle of about 20°, and 

 the fourth descends at an angle of about 70°. The pilei all tend to 

 take up a more or less horizontal position. The result of these diver- 

 gences is that the 

 three highest fruit- 

 bodies, although im- 

 bricating, all have a 

 free space beneath 

 their pilei suffici- 

 ently deep to permit 

 of the wind carrying 

 away the spores 

 falling from the gills 

 before they can 

 settle on the tops of 

 the subjacent pilei. 

 The vertical dis- 

 tance between each 

 pair of pilei is only 

 4-10 mm. How- 

 ever, the spores are 

 so small that they 

 must fall in still air 

 at a rate of less than 

 • 5 mm. per second.^ 

 Assuming the rate 

 of fall to be • 5 mm. 

 per second it is clear 

 that, in still air, 

 the spores of the 

 three highest pilei would fall for 8-20 seconds before settling on 

 the pilei below. A simple mathematical calculation shows that, if 

 the pilei are assumed to be one inch in diameter, a horizontal air- 

 current passing between the pilei at the rate of only one foot per 

 minute would be much more than sufficient to carry away all the 



1 This statement is based on comparative observations of the rates of fall of 

 spores of various sizes. Vide these Researches, vol. i, 1909, p. 175. 



Fig 



160. — Panus stypticus physiological form lumi- 

 nescens — a luminous fungus. Fruit-bodies separated 

 from an imbricating mass. The top one shows the 

 upper surface, the two middle ones show the lower 

 surface, and the bottom one is seen in section. The 

 fruit-bodies were kept dry for six weeks and then 

 revived by wetting their upper surfaces. They 

 then discharged great numbers of spores and at 

 the same time exhibited luminescence. The lower 

 sides of the pilei glowed more strongly than the 

 upper. Obtained from a stump at Ottawa, Ontario, 

 Canada. Natural size. 



