SEX AND HYPHAL FUSIONS 185 



the same time can combine with any number of other mycelia 

 with which it may come into contact, whatever may be their sexual 

 condition. 



In certain other heterothallic species, e.g. Coprinus lagopus, 

 C. niveus, and Schizophyllum commune, the spores and the mono- 

 sporous myceha are of four sexual kinds which may be represented 

 by the symbols {AB), (ah), (Ab), (aB). Of the haploid mycelia, 

 (AB) may unite with (ab) to form a diploid mycelium {AB)-{-{ab), 

 or (^6) may unite with {aB), to form a diploid mycelium {Ab)-\-{aB) ; 

 so that, in each of the species under consideration, there are six 

 possible kinds of mycelia: (AB), (ab), (Ab), {aB), {AB)-]-{ab), 

 and {Ab)-}-{aB). With two sets of mycelia : 



(AB), (ab), (Ab), {aB), {AB)+{ab) {Ab) + {aB). 

 {A'B'), {a'b'), {A'b'), {a'B'), {A'B')+{(i'b'), {A'b')^{a'B'), 



there are sixty-six possible combinations taken two at a time. Of 

 these combinations the following are a few examples : 



{AB) X {A'B'), {AB) X {ab), {AB) x {Ab), {AB) x {aB), 



{AB) X {AB)-\-{ab), {AB) x {A'b')+{a'B'), 



{AB) + [ab) X {A'B')^{a'b'), {AB)+{ab) x {A'b') + {a'B'). 



Twenty-one of the sixty-six combinations were actually made on 

 dung-agar plates, and in every one of them hyphal fusions between 

 the two myceha were observed {vide infra). The union of the two 

 mycelia in the combination {Ab) X {Ab)-\-{aB) is illustrated in the 

 next chapter in Fig. 135. From these observations we are justified 

 in concluding that, in Coprinus lagojjus and similar Hymenomycetes, 

 any two like mycelia or any two unlike mycelia can unite with one 

 another to form a compound mycelium and that, in general, any 

 one kind of mycelium at one and the same time can combine with 

 any number of other mycelia with which it may come into contact, 

 whatever may be their sexual condition. 



From the data which have just been set forth it will be seen that, 

 in the heterothallic Hymenomycetes, the formation of hyphal con- 

 nexions between one mycelium and another has nothing to do with the 

 particular sexual condition of the mycelia concerned. If two mycelia 

 which do not react sexually happen to unite, no association takes 

 place between their nuclei ; but, if two mycelia of opposite sex 



