BASIDIOMYCETES 403 



hypha (Fig. 267, 8). In many species the branches develop later, pref- 

 erably from the clamp. 



Although clamp connections are by their nature connected with binu- 

 cleate mycelium, they appear in exceptional cases, e.g., Stereum hirsutum, 

 in uninucleate mycelium (Kniep, 1919) and in Coprinus narcoticus in 

 multinucleate primary mycelium (Brunswik, 1924). Conversely, the 

 extension of binucleate condition is much curtailed in certain cases. 

 While the clamp connections in Lenzites abietinus, Merulius lacrymans, 

 Daedalea unicolor and Fistulina hepatica are to be found regularly at each 

 septum and are not influenced by conditions of growth; in Coniophora 

 cerebella, Clitocybe expallens, Lepiota rhacodes and Lycoperdon pyriforme, 

 they occur only irregularly. Under natural conditions, they may be 

 numerous in certain stages of development and be lacking in others or 

 in artificial cultures may be made to disappear in submersed mycelium 

 or by other interference. In still other species, as Corticium bombycinum, 

 Armillaria mellea and Calocera viscosa, they are entirely lacking and the 

 dicaryon divides without this indirect mechanism (Rumbold, 1908; Kniep, 

 1913, 1918). The significance of this clamp formation is still obscure and 

 will be discussed along with the phylogeny of the Basidiomycetes. 



The differentiation into main axis and branches, the second character- 

 istic of secondary mycelium, is easily noted in artificial cultures. The 

 main axes are well developed; in contrast to hyphae of the uninucleate 

 mycelium they run almost parallel to each other and lend themselves 

 easily to the formation of rhizomorphs. The branches are smaller and 

 thinner without marked polarity; under abnormal conditions of nourish- 

 ment, however, they may develop into main axes. As in the case of 

 uninucleate hyphae, anastomoses are formed between the branches. In 

 contrast to the anastomoses of the uninucleate hyphae, however, they 

 do not result in developmental stimuli : after the cell fusion, one dicaryon 

 dissolves, leaving the double cell binucleate (Fig. 266, 2). The same 

 thing occurs in the anastomoses of primary and secondary hyphae, where- 

 by the fusion cells occasionally become uninucleate. These fusions are 

 only vegetative (Bensaude, 1918). 



In a large number of higher Basidiomycetes, usually at some distance 

 from the hyphal tip, the divisions of the dicaryons are not followed by wall 

 formation. Consequently, in time, the number of nuclei in these cells 

 mounts as high as twenty, and the cells become ceonocytic, as in the 

 uninucleate mycelium. There proceeds a more or less synchronous divi- 

 sion of these nuclei which is then followed by the formation of septa. 

 In contrast to the coenocytic cells of the primary mycelium, which sepa- 

 rate into uninuclear cells, these coenocytic cells of the binucleate mycelium 

 behave as binucleate cells, in spite of the transitory loss of their binu- 

 cleate character in the different phases of their development. They 

 contain many dicaryons but, by an increasing limitation of the number of 



