HELIOTROPISM OF ASCI IN DISCOMYCETES 321 



not take place below a certain temperature (about 10° C.) ^and, when 

 it does take place, it is accomplished not by a series of vigorous and 

 intermittent puffs but by the successive bursting of asci which 

 results in the Hberation of a stream of spores Uke that which escapes 

 from the pileus of one of the Hymenomycetes. 



Falck found that two fruit-bodies of Morchella esculenta lying in 

 the shade in a cool room had a temperature of 15- 3° C. and were not 

 discharging spores. He thereupon exposed the fruit-bodies to 

 direct sunlight. After one minute a thermometer behind the 

 irradiated hymenium registered 18° C. and spore-discharge had 

 become active. After five minutes the thermometer registered 

 19' 8° C. and spore-discharge continued. He then placed the fruit- 

 bodies in the shade. After four minutes the thermometer registered 

 16-9° C. and the discharge of the spores had ceased.^ These experi- 

 ments strongly support Falck's conclusion that the sun, under 

 natural conditions, must often be a prime factor in causing fruit- 

 bodies, not only of Morchellae but of Gyromitrae, Verpae, and other 

 vernal radiosensitive Discomycetes, to discharge their spores. 



Falck ^ regards the brown colour of the caps of Morchella, Gyro- 

 mitra, etc., as an aid to the absorption of the sun's rays and therefore 

 as advantageous for the working of the spore- discharge mechanism. 



The Helvellaceae. — The Helvellaceae, according to Boudier,* 

 include the following genera : Ptychoverpa, Verpa, Gyiomitra 

 (Figs. 160 and 161), Physomitra, Helvella (Fig. 163, p. 328), and 

 Leptopodia. In all the species of this family the fruit- bodies are 

 stipitate, while the j511eus is attached by its centre to the stipe, is 

 reflexed in the form of a hood, and is more or less lobed. 



Several illustrations of asci of various species of Helvellaceae 

 drawn by Boudier and reproduced in his Icones Mycologicae 

 suggest that the asci of the Helvellaceae are heliotropic. Among 

 these illustrations are: (1) an ascus of Gyromitra gigas ^ with 



^ R. Falck, " Ueber die Sporenverbreitung bei den Ascomyceten. I. Die radio- 

 sensiblen Discomyceten," Mycologische Untersuchungen und Berichie von R. Falck, 

 Bd. I, Heft IT, 1916, pp. 91-92. 



2 Ibid., p. 102. 3 Ibid., pp. 84, 114-115, 125. 



* fi. Boudier, Histoire et Classification des Discomycetes d'Europe, Paris, 1907, 

 pp. 33-38. 



* E. Boudier, Icones Mycologicae, Tome II, PI. 221,/. 



VOL. VI. ^ 



