282 THE BASIDIOMYCETES 



Bella, Clitocybe expallens, and Lycoperdon pyriforme. A whorl 

 of clamps may be developed in Coniophora cerebella. Clamp 

 connections are commonly present also among the jelly fungi. 

 In Armillaria mellea and Corticmm bombycimimy although the 

 cells are dicaryotic, clamps are absent. They occur in the mono- 

 caryotic mycelium of Stereiim hirsiitinn and in the coenocytic 

 mycelium of Copriniis narcoticiis. 



The essentials of the process of clamp formation among the 

 higher Basidiomycetes are as follows: A bowed pouch-like pro- 

 trusion arises from the wall medianly between a pair of nuclei. 

 The nuclei divide conjugately, and one of the daughter nuclei 

 passes into the pouch. A septum is formed near the base of the 

 pouch, producing a uninucleate clamp cell. At the same time 

 another septum is laid down to separate two of the nuclei in the 

 terminal cell from the fourth nucleus in the basal cell. After a 

 time the tip of the clamp cell fuses with the basal cell, and the 

 nucleus of the clamp cell passes out into the basal cell, thus 

 making it binucleate. 



Evidently diploidization may be initiated in several ways. De- 

 tails of the process in Ustilaginales and Uredinales will be con- 

 sidered later in connection with these orders. Among Hymeno- 

 mycetes it may be initiated by the fusion of monocaryotic hy- 

 phae of opposite sexual phases. It may also result by fusion of 

 an oidium borne on a hypha of one sexual phase with the hyphae 

 of the opposite phase [Brodie (1931)], or oidial mycelia of op- 

 posite sexual phase may unite [Brodie (1931)]. Some cases of 

 diploidization are not so readily explained and appear to involve 

 factors for compatibility and their disjunction, and the existence 

 of "geographic races." Newton (1926) found among 25 mono- 

 sporous mycehal cultures of Coprimis rostrupiamis that 11 re- 

 mained haploid, whereas 14 spontaneously became diploid. At 

 any rate mycelial cells once diploid remain diploid throughout 

 the greater period of the developmental cycle, and fusion takes 

 place in the young basidia, whereupon reductional division fol- 

 lows to form haploid basidiospores in the majority of species. 



The development of present-day concepts of diploidization 

 and an interpretation of its significance are comprehensively pre- 

 sented in a report by Buller (1941). 



CoNiDiA. The production of conidia among Basidiomycetes 

 cannot be regarded as of common occurrence'. The basidiospores 



