204 RESEARCHES ON FUNGI 



(AB) and {Ab) cannot interact sexually because they have a factor 

 {A) in common. 



It is obvious that in Coprinus lagopus there are two kinds of 

 diploid myceha, one derived from the combination (AB) X (ab) 

 and the other derived from the combination (^6) X (aB). These 

 two kinds of diploid mycelia may be represented by the symbols 

 {AB)^{ab) and {Ab)+{aB) respectively. 



In what follows, we shall consider the results of pairing a haploid 

 mycelium with a diploid mycelium : (1) when the combinations 

 are (AB) X {AB) + {ab), (ab) X {AB)+{ab), {Ab) X {Ab) + {aB), 

 (aB) X {Ab) + {aB), i.e. when only two kinds of nuclei and all 

 four kinds of sex factors are involved and the combinations seem 

 to be theoretically compatible ; and (2) when the combinations are 

 (AB) x{Ab)+{(tB), (ab) X {Ab)+{aB), {Ab) X {AB)+{ab), and 

 {aB) X {AB)i-{ab), i.e. when three kinds of nuclei and all four 

 kinds of sex factors are involved and the combinations seem to be 

 theoretically incompatible. 



The Pairing of Haploid and Diploid Mycelia.— (1) Preliminary 

 experiments : the two mycelia of equal size. Mr. H. J. Brodie, 

 working in my laboratory, had in culture a number of monosporous 

 mycelia of Coprinus lagopus. Of these his No. 10 and No. 5, which 

 were of opposite sex and to which he had assigned the symbols 

 {AB) and {ab) respectively, were given to me. On mating them, 

 a diploid mycelium {AB)+{ab) was obtained (for the method of 

 mating, ^/. Fig. 110). 



The haploid mycelium {ab) and the diploid mycehum {AB)+{ab) 

 were then paired on dung-agar contained in a Petri dish. The 

 pairing was accompUshed by setting on the dung-agar in the plate, 

 about 1 cm. apart, two small pieces (about 6 square mm.) of dung- 

 agar, one containing the haploid mycelium and the other the diploid. 

 Two days after the beginning of the experiment, the haploid 

 and the diploid mycelia had come together and .hyphal fusions 

 between them were observed. 



After another two days, clamp-connexions were observed on all 

 the leading radial hyphae at the periphery of the {ab) myceUum for 

 a distance of 1 cm. on one side of the {AB)^{ab) mycelium. 



After one more day (five days from the beginning of the 



