374 



CLASS BASIDIOMYCETEAE 



nucleate by the division of the nucleus before discharge. It gives rise to a 

 coenocytic mycelium with cross walls at rather long, intervals. The nuclei 

 divide apparently independently of one another and no conjugate divi- 

 sions can be noted. In the younger mycelium clamp connections arise 

 singly but as the mycelium becomes older they may arise by twos and 

 in still older mycelium in whorls. Their formation has no apparent con- 

 nection with nuclear divisions. From one to several nuclei may pass into 

 each pocket which fuses with the cell below the septum and discharges all 

 the contained nuclei into that cell, or a lateral branch may be formed into 

 which the nuclei pass. Sometimes the terminal cell of the hj^pha is left 

 without any nuclei. The author believes that these whorls of clamp con- 

 nections serve to distribute various types 

 of nuclei to the new branches. (Fig. 125.) 

 The greater prevalence of clamp con- 

 nections in the Basidiomyceteae is probably 

 due in the first place to the fact that in 

 most members of this class the dicaryon 

 mycelium represents a much greater por- 

 tion of the life history of the plant than 

 do the rather transitory or entirely wanting 

 ascogenous hyphae of the Ascomyceteae. 

 Furthermore, in the latter group these 

 hyphae are broader in general, so that at 

 conjugate division the two dividing nuclei 

 may lie side by side instead of some dis- 

 tance apart in the longitudinal axis of a nar- 

 row hypha. Only in the latter case is a by-pass really necessary. Some 

 whole genera of the Basidiomyceteae lack clamp connections entirely. 



The prevalence of clamp connections varies greatly in different parts 

 of the same mycelium and is, furthermore, modified greatly by the en- 

 vironment. Thus mycelium submerged in liquid media may have but few 

 or even no clamp connections while the aerial portions may produce them 

 in abundance. They may be present on the slenderer hyphae m the pileus 

 of the mushroom and absent in the broader extensions or branches of 

 these same hyphae. In some species they are found only at great intervals 

 while in others they occur at every septum. In some species they are only 

 found in the subhymenial tissues of the spore fruit but not elsewhere, even 

 when all the tissues consist of dicaryon mycelium. Hirmer (1920) ob- 

 served conjugate divisions in the mycelium of Agaricus campestris Fr., 

 although clamp connections were completely absent. Within the genus 

 Coprinus Brunswik (1924) has found some species which lack the clamp 

 connections entirely and other closely related species in whose mycelium 

 they are abundant. He interprets this as the gradual loss of a structure 



Fig. 125. Class Basidio- 

 myceteae. Whorls of clamp con- 

 nections in Coniophora puteana 

 (Schum. ex Fr.) Karst. (After 

 Kemper: Zentr. Bakt., Para- 

 sitenk. und Infektionskr. , Zweite 

 Abt., 97(4-8) :100-124.) 



