200 SPORE DISSEMINATION 



From the evidence it seems entirely probable that Uredinales 

 generally are capable of violently discharging their basidiospores. 

 The urediniospores are powdery and are disseminated by wind. 

 Evidently aeciospores in many species are projected out of the 

 aecia with considerable force. Attention was first directed to the 

 matter of forcible ejection of aeciospores by Zalewski (1883) 

 from observations on Uromyces pisi, whose aecia are borne on 

 Euphorbia. He also showed from experiments that Puccinia 

 graminis, P. calystegia, P. coronata, and Aecidium symphyti dis- 

 charge their aeciospores, the oldest, outermost aeciospores of the 

 chain being discharged first. Dodge (1924) observed the same 

 phenomenon in Gymnotelium myricatum and Puccinia podo- 

 phylli. From similar studies Buller (1924) recorded its occur- 

 rence in XJroviyces poae, Puccinia clematidis, P. fraxinata, P. gros- 

 sulariae, P. graminis, P. hieraciata, P. impatientis, P. poarum, P. 

 pulverulenta, and P. urticata. The mechanism by which expulsion 

 is made possible consists of thickenings of the spore walls, which 

 push into the spore wall opposite. These thickenings serve as 

 fulcra, against which the elastic spore walls react. As the upper- 

 most cells approach maturity, the pressure may be suddenly re- 

 leased above, whereupon the aeciospore is shot out. Sometimes 

 masses of spores are expelled. The aeciospores of P. graminis 

 may be discharged to a height of 7 to 8 mm, of Uromyces pisi, 

 15 to 20 mm. Thus far observations have dealt with cupulate 

 and caeomoid aecia, no studies having been made of rostelioid 

 and peridermioid aecia, in some of which the peridial layer reacts 

 to moisture, and the hygroscopic movements of peridial segments 

 expel the aeciospores. 



Spore discharge among Hymenomycetes. Of course the 

 simplest procedure to demonstrate that Hymenomycetes shed 

 their spores is to place the pilei with undersurface downward on a 

 piece of white paper to secure a spore print or to focus a beam 

 of licrht below the fruit body suspended in a closed glass vessel. 

 Practically all our knowledge of violent spore discharge among 

 Hymenomycetes has come from the studies by Buller, conducted 

 over a period of about 30 years and recorded in his Researches on 

 Fungi. In this period he examined numerous genera and species, 

 including such well-known and widely distributed species as 

 Psalliota cavipestris, Coprinus comatus, C. atramentarius, Poly- 

 porus squaviosus, Lentinus lepideus, Psathyrella disseminata, Ar- 



