EFFECT OF DIPLOID ON HAPLOID MYCELIA 247 



The question may now be asked : can a haploid mycelium be 

 diploidised by a diploid mycelium with which it is theoretically 

 incompatible ? Can (1) the haploid mycelia (^4^) and {ah) be 

 diploidised by the diploid mycelium {Ab)-\-{aB) ; and can (2) the 

 haploid mycelia (^6) and {aB) be diploidised by the diploid 

 mycelium {AB)-\-{ab) ? In the combinations : 



[AB) X {Ab)+{aB), 



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



(Ab) X iAB)+{ab), 



{aB) X {AB)+{ab), 



where the diploid mycelium does not contain nuclei of a sex opposite 



to that of the nuclei in the haploid mycelium, can the diploid 



mycelium effect any sexual change in the haploid mycelium ? An 



attempt to answer these questions was made by means of a number 



of experiments which will now be described. 



First Series '^.of Experiments. As indicated in Table V, four 

 large haploid mycelia {AB), {ab), {Ab), and {aB) were each inocu- 

 lated with a theoretically incompatible diploid mycehum. Thus, 

 for example, the haploid mycelium {AB) was inoculated with a 

 diploid mycelium {Ab)-\-{aB) which did not contain any {ab) nuclei 

 and which, therefore, from the prima-facie theoretical point of 

 view, should not be able to effect its diploidisation. 



As a control for the four illegitimate pairings, four legitimate 

 pairings of the type {AB) X {AB)-{'{ab) were also made, and the 

 results of these pairings are indicated in the Table. 



For convenience in reference, combinations of the tyi3e {AB) X 

 {AB)-\-{ab) or {Ab) X {Ab)-{-{aB) will be called legitimate combina- 

 tions and combinations of the type {AB) x {Ab)-\r{aB) or {Ab) X 

 {AB)-[-{ab) illegitimate combinations. 



An inspection of Table V shows that in the illegitimate combina- 

 tions : (1) the diploid inoculum {Ab)-\-{aB) brought about no 

 change in the haploid mycelium {ab) but caused the haploid 

 mycelium {AB) to become diploid (as shown by mode of branching 

 and development of clamp-connexions) one-sixth of the way around 

 its periphery; and (2) the diploid inoculum {AB)-\-{ab) brought 

 about no change in the haploid mycelium {aB) but caused the 

 haploid mycelium {Ab) to become diploid one-half of the way 

 around its periphery. In the legitimate combinations, as shown by 



