138 



RESEARCHES ON FUNGI 



settled some distance from the vertically-placed hymenium. The 

 latter fact I regard as good evidence of spore-projection, but the 

 former, which for some time seemed to yield convincing proof of 

 the phenomenon, has been found by subsequent investigation to 

 be misleading and based upon a curious optical illusion. As a 

 result of further observations and calculations it can be shown 

 that the spores are really projected from the basidia with a high 

 velocity, but nevertheless it is most improbable that one should 

 observe directly the horizontal motion of a spore because it is 



performed too rapidly. 

 The apparent travelling 

 outwards of a spore 

 from the vertically- 

 placed hymenium, 

 which one can observe 

 so easily in Agaricinese 

 and Polyporese, is really 

 no travelling outwards 

 at all. The spores, when 

 seen in motion, are in 

 reality falling vertically. 

 For some months this 

 illusion deceived me, 

 as, indeed, it had de- 



M 



N 



^? 



FlG. 49. Diagram of a tiny cylinder MN on 

 slide S, viewed from above in the direction 



the 



arrow O with the low power of the microscope. 

 ABCD is a section of the cylinder within the 



range of focus. X and Y show the paths of two 

 spores falling vertically. To the right is shown 

 how the section and the paths of the spores appear 

 to the observer. 



ceived others to whom 

 I had shown it. How- 

 ever, the possibility of the apparent fact of horizontal movement 

 of the spores being in some way deceptive, caused me, after a while, 

 to make a careful study of the appearance of vertical surfaces 

 under the microscope. 



A tiny brass cylinder was constructed, placed upright on a glass 

 slide, and observed from above with the low power of the microscope. 

 It was found that, wherever placed in the field, any part of the 

 vertical surface observed appeared to slope at an angle from the 

 vertical. The result of the observations may best be made clear 

 by means of a diagram (Fig. 49). Let MN be the cylinder standing 

 vertically upright on the glass slide S, and let the arrow O indicate 



