ORIGIN OF RUSTS AND SMUTS AND HETEROBASIDIAE 649 



sporidia in damp air while still attached to the promycelium may produce 

 successively secondary, tertiary, and further sporidia, all obliquely 

 perched on short sterigmata from the sporidia below. In addition there is 

 a great tendency toward the production of spore fruits whose cell walls 

 swell and become gelatinous when w^et, although this is not universal-. In 

 the Uredinales we find this in Gymrwsporangium, Coleosporium, Uropyxis, 

 etc., chiefly in the teliospores and their pedicels. In the Auriculariales, 

 Tremellales, Dacrymycetales, and some Tulasnellales so many genera have 

 this character throughout the w^hole spore fruit that they are often 

 grouped under the common name "Jelly Fungi." Both of the foregoing 

 characters are rare in the Eubasidiae. However in Exohasidium the 

 basidiospores may divide transversely and produce external buds but this 

 is scarcely known in any other Eubasidial genera. Scattered here and 

 there are occasional species with gelatinous cell walls but these are 

 marked exceptions. 



If the Thelephoraceae are to be considered as derived from near 

 Tulasnella it must be by the elimination of the cross walls between the 

 main body of the basidium and the four large spore-bearing pockets, ac- 

 companied by a reduction in size of these pockets until finally in most 

 cases these have entirely disappeared leaving merely their apical sterig- 

 mata. In that case the homologues of the ascospores have, as it were, 

 drawn back into the body of the basidium and entirely disappeared. If 

 this is the way that evolution occurred we must still regard the basidio- 

 spores as secondary spores from hypothetical ascospores, as in the Tulas- 

 nellales, etc. 



Let us consider the case if the holobasidium is the more primitive type, 

 as it is beyond controversy the most freciuent in the whole class. We can 

 still derive it theoretically from one of the Pezizales somewhat similar to 

 Ascocorticium, although probably spermatia were still produced, perhaps 

 even in spermogonia. We can imagine that the basidiospores, as suggested 

 by the author on page 647, are ascospores, in some cases provided with 

 true ascospore walls, inside the everted pockets. The sterigmatal ap- 

 paratus for their discharge rnay have to be looked upon as a new develop- 

 ment to permit their being discharged violently, although perhaps this is 

 a modification of the discharge mechanism found in most asci in which 

 four or more spores contained in the ascus are discharged simultaneously 

 or in quick succession through the single opening at the apex of the ascus. 

 This is brought about by the increase of the osmotically produced tension 

 of the ascus wall until it gives way at the apex and the epiplasm and 

 spores are violently ejected. In the new modification as found in the 

 basidium the discharge affects only one spore at a time at the apex of each 

 sterigma. This new habit is clearly not confined to the primary spore for 



