SIGNIFICANCE OF CONJUGATE NUCLEI 



279 



whenever such a division is required to provide an extra nucleus 

 needed in an adjacent haploid cell for the establishment of a second 

 pair of conjugate nuclei. On the other hand, if two nuclei of 

 opposite sex, on coming to be present in one and the same cell, 

 were to fuse together to form 

 a {2n) nucleus, the {2n) 

 nucleus could do nothing to 

 convert an (n) nucleus in an 

 adjacent haploid cell into a 

 {2n) nucleus unless it were to 

 undergo reduction divisions 

 and produce among its pro- 

 geny a nucleus of the right 

 kind to mate with the (w) 

 nucleus in the haploid cell. 

 Obviously it is far simpler for 

 a pair of conjugate nuclei 

 (ri) + (>0 to provide the (n) 

 mate required by an {71) 

 nucleus in an adjacent hap- 

 loid cell than it would be for a 

 {2n) nucleus to do so. 



The diploidisation of a 

 haploid mycelium by a dij)- 

 loid mycelium in Hymenom}'- 

 cetes like Cojprinus lagopus 

 (Figs. 147 and 148) is effected 

 essentially in the same man- 

 ner as the diploidisation of a 

 haploid mycelium by another haploid mycelium of opposite sex. 

 Thus, in the combination {ab) x {AB)-{'{ab), when a hypha of the 

 {ah) mycelium fuses with a hypha of the {AB)-^{ab) mycehum, the 

 {AB) nucleus in the conjugate pair of nuclei in the diploid hypha 

 divides and one of the daughter nuclei moves into the hypha of the 

 {ah) mycelium. The gradual diploidisation of the {ah) mycelium 

 then proceeds in exactly the same manner as that described in the 

 case of the combination of two haploid mycelia {AB) x {ab). 



Fig. 147. — Coprinus lagopus. Diagram sliow- 

 ing a diploid mycelium (AB)-\-{ab) on the 

 left, and a haploid mycelium (ab) on the 

 riglit. In the diploid mycelium note the 

 ])airs of nuclei of opposite sex in each cell, 

 the clamp-connexions at each septum, 

 and the narrow-angled mode of branching. 

 In the haploid myceliiun note tlie single 

 isolated nucleus in each cell, the plain 

 septa devoid of clamp-connexions, and 

 the wide-angled mode of branching. A 

 central liypha of the diploid mycelium is 

 about to fuse with a hypha of the haploid 

 mycelium. The diploid mycelium, after 

 tlie fusion was effected, would begin to 

 diploidise the liaploid mycelium (vide 

 Plates III and IV;. Highly magnified. 



