FREQUENCY OF NUCLEAR DIVISION 243 



not only do the 26,000 end-cells of the (AB) mycelium receive (ab) 

 nuclei, but also several of the subterminal cells of each of the leading 

 hyphae, all the younger lateral branches of the leading hyphae, as 

 well as a great number of the hyphae which are not so peripherally 

 situated (interior hyphae). The number of (ab) nuclei required to 

 effect diploidisation of our large {AB) mycelium is therefore far 

 greater than 26,000 and may well exceed 250,000. 



The Frequency of Conjugate Nuclear Division in a Radial 

 Diploid Hypha. — A leading radial hypha in a diploid mycelium of 

 Coprinus lago]3us growing on dimg-agar in a large Petri dish pro- 

 duced clamp-connexions at very regular distances apart. The 

 average distance between two successive clamp-connexions was 

 found to be 0-18 mm. ; so that, in a hypha 1 -0 cm. long, there are 

 about 55 clamp-connexions. 



A leading radial hypha of a diploid mycelium was kept under 

 observation and was sketched at successive intervals of time during 

 a period of twelve hours ; and thus the number of successive clamp- 

 connexions which it developed was determined. Fourteen clamp- 

 connexions were formed in the twelve hours ; so that, on the 

 average, one new clamp-connexion was formed every fifty minutes. 

 Now it is known from the work of Kniep ^ and Mile Bensaude - 

 that a conjugate nuclear division takes place whenever a clamp- 

 connexion is formed. We may therefore conclude that, in the 

 diploid hypha that was under investigation, a conjugate nuclear 

 division took place every fifty minutes. 



The time required for a single conjugate nuclear division is 

 always a little less than that required for the complete development 

 of a clamp-connexion (r/. Fig. 85, p. 155). A clamp-connexion is 

 formed in much less than fifty minutes, certainly in less than 

 thirty minutes. It may well be that a single conjugate nuclear 

 division takes place in less than fifteen minutes. 



Hyphal Fusions between All Possible Kinds of Mycelia. — From 

 eight spores two complete sets of haploid mycelia {AB), {ab), {Ab), 



1 Hans Kniep, " Beitrage zur Kenntnis der Hymenomyceten, III," Zeitschrift f. 

 Botanik, Bd. VII, 1915, pp. 369-398. 



2 M. Bensaude, Recherches sur le cycle evolutifet la sexualite chez les Basidiomycetes, 

 Nemours, 1918, pp. 1-156. 



