372 



CLASS BASIDIOMYCETEAE 



Very frequently, but by no means universally, associated with the 

 secondary type of mycelium is the production of clamp connections. 

 These are produced more often at every septum in the more slender 

 hyphae but may be absent on a portion of the same hypha where the cells 

 are broader. This has been frequently noted by the author in the tissues 

 of the pilei of various Agaricaceae, where slender hyphae bearing clamp 

 connections may as they elongate produce a series of broader cells without 

 these structures and perhaps still further on becoming slender again 

 bearing clamp connections. On the other hand even these broader hyphae 

 may show clamp connections, as illustrated in some of the figures by 

 Ktihner (1926) though other figures show the broader hyphae without 



n 



I 



r\ 



+ y* o 



r\ 



r\ 



.^ 



Fig. 124. Class Basidiomyceteae. Diagram- 

 matic representation of the steps in the for- 

 mation of clamp connections. (Courtesy, Ben- 

 saude: Recherches sur le cycle evolutif et la 

 sexualite chez les Basidiomycetes, Nemours, 

 published by author.) 



such structures. Whenever clamp connections are present the mycelium 

 is thereby indicated as being dicaryotic, i.e., of the secondary type, but 

 from the foregoing it is evident that the absence of these structures does 

 not in all cases indicate the primary monocaryon nature of the hyphae. 



The mode of development of clamp connections was reported inde- 

 pendently by Kniep (1915) and Mile. Bensaude (1918). The details of the 

 formation are as follows : The two nuclei of the terminal cell of a dicaryon 

 hypha lie a short distance apart in the longitudinal axis of the cell. Be- 

 tween them a lateral pocket is formed in the wall. The two nuclei now 

 divide simultaneously (conjugate division) and the lower daughter nu- 

 cleus of the upper pair passes into the pocket. This is now cut off from 

 the main cell by the formation of a septum. At the same time the upper 

 daughter nucleus of the lower pair, lying at about the level of the upper 

 end of the pocket becomes separated from its sister nucleus by a trans- 



