THE FUNGI: ASCOMYCETES AND BASIDIOMYCETES 325 

 Spore Discharge 



The four spores on a basidium are not all shed together, but successively, 

 a few seconds or minutes after one another. A few seconds before the spore 

 is actually shed a drop of liquid appears at the tip of the sterigma. This drop 

 has a diameter about half that of the spore and is shed with the spore. The 

 spore therefore is very adhesive when first liberated. Each spore is shot off 

 horizontally a distance of about ^1^ in. (o-i mm.), and it is probably the 



Fig. 318. — Psalliota ctniipestris. Spore print on paper, 

 deposited from a ripe pileus. 



vacuolation of the basidium referred to above which provides the necessarv 

 force. The motion is at first more or less horizontal in the space between 

 the gills, but, due to air resistance, this movement is soon brought to a stop 

 and the spore begins to fall under the action of gravity. The fall is most 

 rapid while the spore is still between the gills, but after about a minute it 

 dries and the reduction in volume appears to reduce the rate of fall, which 

 depends on the size and specific gravity of the spore. The rate of fall varies 

 from -^^-^ to I in. (0-3 to 6 mm.) per second (Fig. 318). 



This peculiar method of spore discharge has an important bearing on the 

 structure of the fruiting body. The violent expulsion ensures that the spore 

 shall be shot clear of neighbouring basidia and will then fall freely between 

 the gills, provided that they are vertical. A tilt of 2° 30" out of the vertical 

 is said to be sufficient to prevent some of the spores escaping, while at 5° 

 half the spores will fall on the adjacent gill plates, and w'ith a tilt of 9° 30" 

 four-fifths of the spores will fail to reach the exterior. These facts will 

 explain why the fruiting body of a mushroom so rapidly orientates itself to 

 the vertical if placed at an angle. Moreover it can be shown that it oscillates 

 about the vertical before finally coming to rest. In some species in which 



