SPORE DISCHARGE AMONG BAS1DIOMYCETES 



191 



charge, because the drop is a hemispherical mass in contact with 

 the spore. If the surface tension between the surface of the spore 

 and the drop is considered negligible, the surface energy of the 

 hemispherical drop is 0.0000095 erg. Then the difference between 

 0.000012 erg and 0.0000095 erg is 0.0000025 erg. This energy is 

 calculated to be seven times that necessary for the actual initial 

 velocity of the spore when it is 

 liberated. Ingold (1939) explains 

 how this energy is mobilized to 

 break the connection of the spore 

 with the sterigrna and to dis- 

 charge it as follows: "At the mo- 

 ment of spore discharge the drop 

 excreted at the hilum flows to the 

 side of the spore, and, while this 

 is happening, the spore will tend 

 to move in the opposite direction. 

 This would involve pressure of 

 the spore on the end of the 

 sterigma. This pressure, sud- 

 denly exerted, might lead to the 

 springing of the spore into the 

 air just as one jumps from the 

 ground by pressing suddenly 

 downward. . . . Only a small 

 fraction of the available surface- 



Fig. 35. Spore discharge, in dia- 

 gram, of Psalliota ccnnpestris. 

 (After Ingold.) A, spore on 

 sterigma, B, just before discharge. 

 The exuded droplet of liquid, C, 

 is of full size. During discharge 

 the drop, C, takes up position, D, 

 and is carried away on the side 

 of the basidiospore. 



tension energy is required to im- 

 part the necessary initial velocity to the spore, and the remainder 

 is available for breaking the connection between the spore and 

 its sterigma." 



Spore discharge in smuts. The chlamydospores of smuts are 

 pulverulent, except in a few species. Air currents constitute the 

 primary factor in the dispersal of these spores. Forcible expulsion 

 of sporidia has not been noted among the Ustilaginaceae. Among 

 the Tilletiaceae, however, Buller (1933) and his associates have 

 studied violent spore discharge in Tilletia tritici, T. laevis, T. hor- 

 rida, T. hold, T. asperifolia, Entyloma ?nemspermi ? E. lobeliae, 

 and E. linariae. When a chlamydospore of these species germi- 

 nates, a short mycelium, generally regarded as the basidium, is 

 produced. At the tip of this mycelium a cluster of about a dozen 



