HELIOTROPISM OF ASCI IN DISCOMYCETES 265 



outer surface of the hymenium, so 

 by their prominent summits, and 

 it has long been kno^\^l that these 

 protuberant asci bend toward the 

 Hght and are therefore positively 

 heliotropic. Zopf ^ illustrated the 

 heliotropism of the asci of Asco- 

 bolus denudatus and of a species of 

 Saccobolus in his well-known text- 

 book in 1890 (Figs. 125 and 126). 



As a result of my own obser- 

 vations, I have no doubt that 

 the asci of Ciliaria scutellata, 

 Aleuria vesiculosa, Galactinia 

 badia, Morchella crassijies, and 

 other similar Discomycetes, like 

 those of the Ascoboleae, are heho- 

 tropic, and that the response of 

 the asci to the directive stimulus 

 of light serves to explain how it 

 is that the ascospores discharged 

 from the interior of hollow cups, 

 such as those of Aleuria vesiculosa, 

 Galactinia badia, etc., and from the 

 interior of cavernous depressions 

 at the surface of the caps of the 

 Morchellae are shot out into the 

 external air without striking op- 

 posing chamber walls. 



In the summer of 1926, at the 

 International Congress of Plant 

 Sciences, I gave a paper ^ on the 

 discharge of spores in the Higher 



that the disc is made papillate 



Fig. 125. — Ascobolus denudatus. Helio- 

 tropism of the asci. A, a smaller 

 and a larger cup-like fruit-body on 

 a fragment of dung. The asci pro- 

 truding above the hymenium have 

 all become heliotropically bent 

 toward the light, the direction of 

 which is indicated by the arrow. B, 

 a vertical section through one of 

 the fruit-bodies showing the hy- 

 menium in which are the lieliotropi- 

 cally bent asci, each containing 

 eight spores. C, a single ascus 

 from B ; it is strongly bent toward 

 the source of the light. The dotted 

 line indicates the top of the hy- 

 menium. Drawn by W. Zopf. 

 From his Die Pilze (1890, p. 205). 

 Magnification : A, 25 ; B, 80 ; 

 C, 300. 



1 W. Zopf, Die Pike, Breslau, 1890, pp. 205-206, Fig. 64. 



2 A. H. R. Buller, " Some Observations on the Di.scharge of Spores in the Higher 

 Fungi," Proceedings of the International Congress of Plant Sciences, Vol. II, 1929, 

 pp. 1627-1628, 



