348 PHYSIOLOGY OF THE FUNGI 



The force which causes the discharge is apparently located in the 

 palisade layer. It has been demonstrated by microchemical tests that 

 the palisade cells of the unopened fruit body are densely filled with 

 glycogen, which disappears before the discharge of the peridiole (Walker 

 and Andersen, 1925). The glycogen is converted to reducing sugars, one 

 of which is maltose, and this leads to the increase in osmotic pressure. 

 Light hastens the opening of the fruit body and the discharge of the 

 peridiole and is believed to speed up the conversion of glycogen into 

 sugars. S. stellatus is a coprophilous or lignicolous species, and the 

 peridioles may be eaten and disseminated by herbivorous animals. 



Dodge (1941) reports his own observations as well as those of others 

 upon the presence of peridioles of the bird's-nest fungi attached to leaves 

 and branches as high as 10 to 15 ft. above the ground. Dodge describes 

 the attachment of the peridioles of Cyathus striatus to the peridium but 

 offers no theory to explain the mechanism of the peridiole discharge or 

 the force which is responsible. The slender mucilaginous threads which 

 attach the peridioles in the fruit bodies also serve to attach the discharged 

 peridioles to certain objects. 



Discharge of basidiospores. The mechanism and the force involved 

 in the discharge of basidiospores in the Hymenomycetes and of the 

 sporidia of the smuts and rusts have not been satisfactorily explained. 

 There is no evidence that the explanation used for any of the types 

 described above can be applied to the discharge of basidiospores. How- 

 ever, certain structural features are present which may be adaptations 

 for this special method of spore discharge. 



In all Basidiomycetes in which the spores are shot off forcibly, the 

 sterigma is attached slightly to one side of the tip of the spore (Fig. 72). 

 Just before a spore is discharged, a small drop of liquid appears at the 

 tip of the sterigma. Its invariable presence is believed to be an important 

 feature in the process of spore discharge. After discharge, there appears 

 to be no pore present, either in the spore or in the tip of the sterigma. 

 Buller (1922, 1924) suggests that the spore may be shot from the sterigma 

 by hydrostatic pressure, but that the amount of liquid ejected as the 

 explosion occurs at the sterigma may be so minute that it may not be 

 detected by the microscope. He further suggests that the surface ten- 

 sion of the drop of water may in some way bring about the abjection of the 

 spore. While neither theory is completely satisfactory, they are the best 

 yet offered. 



Discharge of aeciospores. Experimental work showing that the 

 aeciospores of the rust fungi are violently discharged was reported by 

 Buller (1924) and Dodge (1924, 1924a). They have reported this phe- 

 nomenon in seven species, including Puccinia coronota, P. graminis, P. 

 podophijlli, Gytnnoconia peckiana, and Uromyces pisi. The maximum 



