BASIDIOMYCETES 401 



With the first conjugate division of the dicaryon, clamp connections 

 are formed in Coprinus fimetarius and Peniophora Sambuci. In other 

 species, ' as Typhula erythropus (Lehfeld, 1923), the relationships 

 appear to be more complicated. In these, the anastomoses do not 

 immediately succeed the germination of the basidiospores, but later when 

 the primary haploid mycelia have reached a definite point of development 

 (sexual maturity); thereby the relationships become obscure. Further, 

 plasmogamy does not lead directly to the formation of a dicaryon, but 

 the migrating nucleus passes (in several divisions) through the new, unre- 

 lated hypha, whereby the septa are dissolved and thereafter are partially 

 regenerated. Suddenly clamp connections appear in different places, 

 often at some distance from the anastomosis. These develop laterally 

 into binucleate mycelia. 



This new binucleate mycelium formed by plasmogamy is called second- 

 ary mycelium, in contrast to the earlier uninucleate mycelium. It is 

 differentiated from the primary mycelium by the formation of clamp 

 connections, by its differentiation into main axis and branches, by the 

 vegetative character of its anastomoses and by the virtually binucleate 

 character of it coenocytic cells. 



The clamp connections arise as follows : Before the dicaryon prepares 

 to divide, a small, bow-shaped outgrowth is formed usually in the middle 

 of the cell between the two nuclei (Fig. 267, 1). The two nuclei move to 

 the place of branching and one of them penetrates a distance into the 

 clamp while the other remains behind in the base of the clamp (Fig. 267, 

 2); whereupon they begin conjugate division (Fig. 267, 3 and 4). The 

 axis of the spindle of one nucleus lies in the direction of the main hypha, 

 the axis of the other spindle lies obliquely in the clamp. Before the four 

 daughter nuclei have completed the telophase, two go toward the end of 

 the hypha, one goes basipetally and the fourth remains in the clamp (Fig. 

 267, 5). The two nuclei of the developing end of the hypha are separated 

 from the basal cell (previously uninucleate) by a septum which is formed 

 directly under the base of the clamp ; the nuclei are arranged in the usual 

 manner in the middle of the cell. The uninucleate clamp cell is cut off 

 from the terminal cell by a second septum which forms with the first an 

 oblique angle, opening apically (Fig. 267, 6). After a short time, the 

 end of the clamp cell fuses with the uninucleate basal cell into which its 

 nucleus migrates (Fig. 267, 7). Thus the basal cell gains its usual binu- 

 cleate condition. In this relationship, however, many anomalies occur; 

 the fusion of the clamp cell with the basal cell may be retarded or entirely 

 omitted, in which case the clamp nucleus degenerates; or the formation of 

 the septa may be retarded or may take place in unusual sequence. Still 

 further, in Coniophora (Fig. 269, 1) and Stereum at the same septum, there 

 appear whole whorls of clusters of clamps whose method of development 



