EFFECT OF DIPLOID ON HAPLOID MYCELIA 253 



After it had been observed in three successive sets of experiments 

 that the diploid myceUum {AB)+{ab) had diploidised (caused 

 clamp-connexions to develop on) the haploid mycelium (Ab) and 

 that the diploid myceUum {Ab)-\r{aB) had diploidised the haploid 

 mycelium (AB), it was deemed advisable to re-mate the original 

 haploids {AB), {ab), {Ab), and {aB) from which the two diploid 

 mycelia had been made, to find out whether or not they would still 

 mate with one another in the usual manner. Therefore the 

 following six combinations of equally large mycelia were made on 

 dung-agar in Petri dishes : 



Legitimate. Illegitimate. 



{AB) X {ab) {AB) X (^6) 



(^6) X {aB) {AB) X {aB) 



{ab) X {Ab) 

 {ab) X {aB) 



It was found that, in the legitimate combinations, both of the 

 haploid myceha soon became completely diploid whereas, in the 

 illegitimate combinations, both of the haploid myceha remained 

 completely haploid. 



Since the diploid mycelium {AB)+{ab) was able to diploidise 

 the haploid mycehum (^6), one might have expected that one or 

 other of the components which were employed to form the diploid, 

 i.e. the haploid mycelium {AB) or the haploid mycelium {ab), would 

 have been able to diploidise the haploid mycelium {Ab) ; but this 

 supposition, as we have seen, did not receive any experimental 

 support. 



Since it was found that a haploid mycelium {Ab) could be 

 diploidised by the diploid mycelium {AB)-\-{ab), but not by the 

 haploid mycelium {AB) or by the haploid mycehum {ab), the 

 following question arose : in general, in illegitimate combinations, 

 does a diploid mycelium act on a haploid mycelium in a manner which 

 is different from that of either of the two haploid mycelia which pro- 

 duced it ? An attempt to answer this question will be made in the 

 third and last series of experiments described in this Section. 



Second Series of Experiments. Since the first series of experi- 

 ments had yielded such an unexpected result, namely, the diploidi- 



