SPORE DISCHARGE AND DISSEMINATION 345 



embedded in mucilage, and as they accumulate in the body of the peri- 

 theciu.m, some spores ooze out through the ostiole, much like tooth paste 

 from the tube. Examples of this type are Chaetomium spp., Cerato- 

 stomeUa fimhriata, and C. ulmi. These spores are not adapted to wind 

 dissemination but may be carried in moist weather by insects (C. ulmi), 

 by other contacts (such as C. fimhriata on stored sweet potatoes), or by 

 rain. 



The Discomycetes, in general, show a marked response to the stimulus 

 of light in orienting the asci so that the ascospores may be discharged 

 into the air away from the apothecium. The apothecium of Ascobolus 

 is small, and only a few asci mature at one time. As an ascus matures, 

 it enlarges greatl}^ and extends well beyond the surface of the hymenium. 

 It then reacts phototropically so that the tip is pointed directly toward 

 the source of light. When the ascus bursts, the operculum at the tip is 

 forced open, and the spores are expelled simultaneously. Most species 

 of Ascobohis are coprophilous and are disseminated in much the same 

 manner as Piloholus and Sordaria. 



The phenomenon of ''puffing" in manj^ of the larger Discomycetes is 

 described in most textbooks of mj^cology and plant pathology. It is due 

 to the simultaneous violent spore discharge from many asci, so that a 

 cloud of spores may be seen to rise a few inches from the apothecium. 

 This may be so violent that a faint hissing or fizzing sound can be heard. 

 If the asci were to explode singly as they mature, the ascospores would 

 be shot up into the air only bj^ the initial force of the explosion. For most 

 species, this distance would probably not exceed 1 or 2 in. However, 

 when a great many asci explode simultaneously, an air blast is created 

 which carries the ascospores vertically to a much greater height, as great 

 as 5 to 7 in. (Buller, 1934). This additional distance above the fruit 

 body, which is commonly located on or near the ground, increases the 

 chances of dissemination by air currents. 



In nature, the puffing of ascospores may be initiated by a sudden 

 change from shade to open sun, by the passing of a cloud, or by swaying 

 of a branch. Strong sunlight is not the only stimulus, for the phenomenon 

 has been observed in the laboratory under uniform light conditions. A 

 sudden jar of the fruit body, when it is tapped or picked up, may cause 

 spore discharge in some species. Likewise, an instant's exposure to 

 alcohol fumes may serve as the stimulus. 



Buller (1934) has shown that in the cupulate or V-shaped apothecia, 

 such as those of Sarcoscypha protracta, many of the asci are pointing 

 directly toward the opposite side of the cup; yet the ascospores are dis- 

 charged upward, free from the fruit body. The operculum of this species, 

 instead of being centrally located at the tip of the ascus, is obliqueh^ 

 placed toward the upper side of the ascus. As the discharged ascospores 



