CHAPTER I 



THE DISPERSION OF SPORES BY THE WIND IN ASCOMYCETES— 

 PUFFING— THE PHYSICS OF THE ASCUS JET IN PEZIZA— THE 

 FIXATION OF THE SPORES IN THE ASCUS OF PEZIZA 11EPANDA 

 —COMPARISON OF THE SIZES OF WIND-BORNE SPORES IN 

 ASCOMYCETES AND HYMENOMYCETES— THE HELVELLACE^E. 



Not only in the Hymenomycetes, but also in many other fungi, 

 beautiful adaptations are to be found by which the spores are 

 suitably dispersed, but in most instances the mechanism involved 

 still awaits a careful analysis from the point of view of physics. 



In the majority of the Ascomycetes, the ascus is an explosive 

 mechanism of considerable power, and it often shoots out its spores 

 to a distance of one or several centimetres, thus causing them to 

 become effectively separated from the sporocarp. It was pointed 

 out in the first chapter of Part I. that the profound differences 

 between Hymenomycetes and Ascomj^cetes in the position occupied 

 by the hymenial surfaces, and in the structure of the fruit-bodies, 

 are correlated with the equally profound differences between 

 basidia and asci as spore-discharging mechanisms. 



The dispersal of ascospores after ejection from the ascus appears 

 in many cases to be brought about either by the wind or by her- 

 bivorous animals. I regard it as a distinct matter of importance 

 which of these two means of dispersal is employed, for each of 

 them is associated with a particular type of ascus. As examples 

 of Ascomycetes with wind-dispersal may be mentioned Gyromitra 

 esculenta, Morchella gigas, Bulgaria polymorpha, and Peziza 

 aurantia, whilst Ascobolus immersus and Saccobolus may be 

 regarded as representing those forms which are spread by her- 

 bivorous animals. It is probable that there are some species of 

 Ascomycetes which have an intermediate type of spore-dispersal, 

 corresponding to that associated with coprophilous Hymenomycetes, 

 in which the spores are first scattered by the wind and subsequently 



