DIPLOIDISATION OF A HAPLOID HYPHA 239 



Fig. 133. — Coprinus lagopus. Progressive transformation of part of a large haploid 

 mycelium (ah) into a diploid mycelivim (AB)-\-{ab) by nuclei derived from a 

 small inoculum (AB). The arrival of the (AB) nuclei in the mycelium and the 

 establishment of pairs of conjugate nuclei is indicated by the formation of 

 clamp -connexions. 



The large haploid mycelium (ah) was grown on dung-agar in a Petri dish ; 

 and, when it had attained a diameter of about 5 cm., it was inoculated at its 

 periphery with a tiny hyphal mass of inoculum (AB). (Cf. Fig. 124, p. 215.) 

 Three days afterwards diploidisation had advanced most of the way around 

 the periphery of the (ah) mycelium proceeding away from the inoculum on 

 both sides (cf. Fig. 128, p. 222). A transition place at the periphery of the 

 (ab) mycelitmn was found where on one side toward the inoculum all the 

 hyphae were already in the diploid phase (provided with clamp-cormexions) 

 and on the other side away from the inoculum all the hyphae were in the 

 haploid phase (devoid of clamp-connexions). At this place a leading radial 

 hypha of the (ab) mycelium was observed which was being converted from the 

 haploid phase to the diploid phase, and this hypha, marked a in the illustration, 

 is shown in three stages of development. It was about 6 cm. distant from the 

 inoculum, it grew in contact with the surface of the dung-agar, and it was 

 drawn with a magnification of 132. 



Stage A. The leading radial hypha a has eight elongating branches, 

 Nos. 1-8, and one very tiny branch (unnumbered) which grew no further. 

 The branch-hyphae Nos. 2, 3, and 4 have already become diploidised, for 

 each of them has developed a clamp-connexion. The branch-hypha No. 1 

 has a side-branch with a clamp-connexion. It is likely that an (AB) nucleus 

 travelled along the diploid hypha b into the branch-hypha No. 1, via the short 

 bridging hypha between b and No. 1, and th\is supplied a conjvigate mate for 

 an (ah) nucleus in the side-branch which shows the clamp-connexion. The 

 branch-hypha No. 3 is abnormally coiled about itself. The hypha a is branched 

 in the wide-angled haploid manner, and it is evident from the disposition of 

 the clamp-connexions on its branches that it is londergoing diploidisation form 

 its older to its younger parts. 



Stage B. Drawn 2 hours and 10 minutes after stage A. Three of the 

 side-branches of the branch-hypha No. 1 now bear clamp-connexions, and 

 additional clamp-connexions have developed on branch-hyphae Nos. 2, 3, 

 and 4. Branch-hyphae Nos. 5 and 6 have now become completely diploidised 

 and are developing clamp -connexions in acropetal succession. On No. 6, 

 between d and the number 7, a clamp-connexion has developed on the main 

 axis far from the growing point, which is somewhat unusual. The last clamp- 

 connexion to appear on No. 6 was the terminal one. The hyphae c and d are 

 lateral branches of other leading radial hyphae not shown in the illustration ; 

 they have become united, by means of bridging hyphae, with the main axis 

 of a and with the branch-hypha No. 6, respectively. Again it is evident that 

 the hypha a is undergoing progressive diploidisation from its older to its 

 younger parts. 



Stage C. Drawn 4 hours and 10 minutes after Stage A and 2 hours after 

 Stage B. The branch-hyphae Nos. 7 and 8 and also two newly-developed 

 branch-hyphae Nos. 9 and 10 now bear clamp -connexions and tlierefore have 

 become diploidised, and a clamp -connexion has at last appeared on the main axis 

 of the hypha a near its growing point. Thus the hypha a with all its ten branches 

 has now become completely diploidised. It was originally part of a haploid 

 myceliimi (ab) ; but now, as a result of the entry into it of (AB) nuclei wliich 

 have formed conjugate mates with its own (ab) nuclei, it has been transformed 

 into part of a diploid mycelium (AB)-}-(ab). 



The progressive conversion of the mycelium into a three-dimensional net- 

 work is evident from a comparison of the drawings A, B, and C. In A there 

 is one hyphal fusion, in B there are three, and in C there are six. Drawn by 

 A. H. R. Buller and Ruth Macrae. Magnification, 88. 



