SPORE DISCHARGE AMONG BASIDIOMYCETES 199 



basidiospores are propelled to a vertical height of 1 .0 mm and to a 

 horizontal distance of 1.4 mm. 



Spore discharge in rusts. Klebahn (1904) is the first investi- 

 gator to point out that the basidiospores of rusts are forcibly dis- 

 charged. Dietel (1912) later recorded the same phenomenon in 

 connection with Puccinia malvacearum, P. glechomatis, P. annu- 

 laris, Coleosporhmi campamdae, C. petasitidis, and Cronartium 

 asclepiadeam. In some instances he observed that a tiny droplet 

 of water appears at the tip of the sterigma immediately before 

 discharge. He determined that under normal conditions basidio- 

 spores may be shot about 0.3 mm vertically and 0.6 mm horizon- 

 tally. For Gy?nno sporangium juniperi-virginianae Coons (1912) 

 recorded a horizontal distance of discharge of 0.26 to 0.36 mm. 

 Shortly thereafter Buller (1924) made a detailed study of spore 

 discharge, especially in Puccinia graminis and Endophyllum 

 euphorbiae-sy haticae. In all essential features the phenomena of 

 discharge among the Hymenomycetes, which he had previously 

 studied, and those in the Uredinales are alike. As differences be- 

 tween the two groups, he notes that the rust basidiospores are 

 larger and are usually shot farther, the distances being 0.4 to 0.85 

 mm in the rusts and 0.05 to 0.2 mm in the fleshy Hymenomycetes. 

 In correlation with these differences he noted that the droplet 

 of water exuded at the spore hilum in Uredinales is somewhat 

 larger and requires from 10 to 40 seconds to form, whereas in 

 Hymenomycetes only 5 to 10 seconds is usually required. 



Later Prince (1943) reported that expulsion of basidiospores by 

 Gymno sporangium nidus-avis is accomplished by a different 

 mechanism from that described by Buller for other rusts. Prince 

 concluded that the mechanism is quite like that among Entomo- 

 phthoraceae. The basidiospore arises as an enlargement of the 

 apex of the sterigma, so that the primary membrane is common 

 to the spore and the sterigma. When the spore attains mature 

 size, a septum is formed in the sterigma that delimits the spore and 

 leaves an apiculus at its base. Next a wall is laid down inside the 

 spore and also one below the septum. Pressures built up in the 

 apiculus of the basidiospore and in the apex of the sterigma rup- 

 ture the primary membrane at the septum, and the instantaneous 

 opposed bulging of the end of the apiculus and of the sterigma 

 results in forcible discharge of the spore. 



