22 RESEARCHES ON FUNGI 



Lycopodium fell with a velocity which was only about one-half of 

 that required by theory. The fraction for the spores of Lycoperdon 

 was about four-sevenths and that for Polytrichum about two- 

 thirds. Zeleny and M'Keehan were unable to account for the want 

 of agreement between fact and theory in the fall of dry spores. 

 There is therefore room for further experiments in this direction. 

 It is of some biological advantage that spores should fall but very 

 slowly in still air. Possibly dry spores have some peculiarity in 

 their construction, yet to be found out, which serves in a special 

 manner to reduce the rate of fall to a minimum. 



The Mechanism of Spore-discharge. The exact nature of the 

 mechanism by which the spores are shot violently from their 

 sterigmata still remains a mystery. In Volume I, I showed that 

 the mechanism is not like that of asci : the basidium does not 

 explode and squirt the four spores away. I suggested that the 

 spores are discharged in the same manner as those of certain 

 Entomophthoraceae. In these fungi a double membrane is formed 

 between the spore and its basidium. At the moment of discharge 

 these two membranes separate from one another, and each, owing 

 to the osmotic pressure in the spore and in the basidium, suddenly 

 becomes convex towards the other. The spore is thus jerked away. 

 However, I pointed out that, for the Hymenomycetes, no one 

 has ever seen any double membrane separating a spore from its 

 sterigma. The neck of a sterigma where it joins the spore has 

 so small a diameter that an optical difficulty prevents one from 

 directly seeing what it contains. 1 



I am now inclined to believe that no such double membrane 



1 W. E. Hiley, in describing the liymenium of Fames annosus (The Fungal 

 Diseases of the Common Larch, Oxford, 1919, pp. 103-104), says : " Each spore is 

 attached to the basidium by a very thin extension of the latter called a sterigma 

 (Fig. 41, B, s<) an d when ripe the spore which develops at its extremity is cut off 

 from the sterigma by a transverse septum . . . the ejection is accomplished by the 

 splitting of the septum between the spore and the sterigma" ; and in his Fig. 41 

 he shows a diagram of a sterigma with a septum across the sterigmatic neck. Hiley's 

 account of the septum in Fomes annosus appears to be based on theory rather than 

 on actual observation ; and his diagram is evidently imaginary, for the sterigma 

 is represented as being curved convexly toward the basidiurn-axis, instead of con- 

 cavely as it should be, with the result that the attachment of the sterigma to the 

 hilurn of the spore is incorrectly illustrated. 



