270 RESEARCHES ON FUNGI 



caused by the same means as those of Sarcoscypha 23rotracta, i.e. they 

 are not warm-air and water-vapour currents, but are produced 

 mechanically by thousands of spores violently striking the air in 

 the same general direction and at the same time, and thus setting 

 the air in motion. 



To explain the phenomenon of pufhng in Morchella and Gyro- 

 mitra, when the fruit-bodies are warmed, we have only to suppose : 

 (1) that the asci are sensitive to heat and, when ripe, always explode 

 when their temperature is raised above a certain degree, so that 

 pufhng may be initiated by warming a fruit-body ; (2) that the 

 asci are curved heliotropically toward the mouths of the hymenial 

 cavities instead of being straight ; and (3) that the air-currents 

 which arise at the moment of puffing are due to the spores and 

 ascus sap-drops bombarding the air and setting it in motion 

 mechanically and are not due to the fruit-body sending out blasts 

 of warm air. 



In what follows an attempt will be made to show how spore- 

 discharge takes place in a number of the commoner Discomycetes 

 which have heliotropic asci. 



The Heliotropism of the Asci of Ascobolus magnificus. — For the 

 purpose of verifying and extending Zopf's statement that the asci 

 of certain Ascoboleae are positively heliotropic, I have investigated 

 the effect of light on the direction of growth of the asci of Ascobolus 

 magnificus. 



Ascobolus magnificus, originally described by B. O. Dodge ^ from 

 North America, occurs on horse dung and, as its specific name 

 indicates, is remarkable for the great size of its fruit-bodies. 

 Dr. Dodge kindly supplied me with cultures of the mycelium. 



When spores of Ascobolus magnificus have been sown on sterilised 

 horse dung in a warm laboratory, the fruit-bodies begin to appear 

 on the surface of the dung at the end of seven days, are about half- 

 grown at the end of ten days (Fig. 129), and are fully grown and 

 expanded at the end of about fourteen days (Fig. 103, Vol. IV, 

 p. 179). Mature fruit-bodies have a flat pale-greenish-yellow 

 hymenium which becomes darkened with protuberant asci containing 



1 B. O. Dodge, "Artificial Cultures of Ascobolus and Aleuria," Alijcologia, 

 Vol. IV, 1912, pp. 218-221. 



