324 RESEARCHES ON FUNGI 



of Verpa in that it is folded into numerous longitudinal and rather 

 freely anastomosing ribs, and the asci are remarkable in that they 

 each contain two very large spores (15-18 X 60-80 y., Seaver i) 

 instead of the usual eight relatively small spores. 



On May 21, 1932, my colleague, Dr. G. R. Bisby, kindly brought 

 to me from the grounds of the Manitoba Agricultural College several 

 rather old fruit-bodies of Ptychoverpa bohemica. I cut transverse 

 sections through their pilei, examined these sections under the 

 microscope, and at once perceived that in all the hymenial grooves 

 and depressions the asci were curved outwards so that their oper- 

 cula must have faced the strongest rays of light to which the 

 ends of the asci had been subjected in the places where the fruit- 

 bodies developed. Thus clear evidence was obtained that in the 

 Helvellaceae, just as in the Morchellaceae, the asci are heliotropic. 



Concluding Remarks. — From the investigations which have been 

 recorded in this Chapter, we may conclude that, in a large number 

 of Discomycetes belonging to various families : (1) the asci are 

 positively heliotropic ; and (2) this response to the stimulus of light 

 is of biological significance in that it permits of a fruit-body pointing 

 and discharging its asci toward open spaces, thus increasing the 

 chances that the spores will be carried off and be dispersed by the wind. 



It is not without interest to note that, while in the Discomycetes 

 heliotropism of the asci is a common phenomenon, in the Hymeno- 

 mycetes heliotropism of the basidia is unknown. The ends of the 

 basidia on the sides of the gills of the Agaricaceae and on the sides 

 of the hymenial tubes of the Polyporaceae are of necessity illuminated 

 from below, and yet they never turn downwards. Owing to the 

 peculiar organisation of the fruit-bodies in these Hymenomycetes 

 and to the very short range of the basidial guns, it is easy to see 

 that a heliotropic response on the part of the basidia would not aid 

 the escape of the spores from the hymenium into the interlamellar 

 or tubular spaces but would actually hinder it. Thus, where a 

 heliotropic response by a fungus gun is advantageous for spore- 

 dispersal, as it is in the Discomycetes, it takes place ; and, where 

 it would be disadvantageous for spore-dispersal, as in the 

 Hymenomycetes, it does not take place. 

 ^ F. J. Seaver, The North American Cup-fungi (Operculates), New York, 1928, p. 244. 



