12-5 THE YEAST CELL 



Bensuade discovered that the clamps (which indicate a dicary- 

 otic mycelium) insure the production of cells, each of which con- 

 tains two complementary nuclei. 



Vandendries discovered that when two mycelia with common B 

 factors are in opposition, they grow to within a few millimeters of 

 each other and then stop without mingling due to some inhibiting 

 substance. He named this phenomenon "barrage." 



Brunswik made an elaborate study of mating type specificity in 

 about 20 species of Coprinus. He found great differences from the 

 classical type of clamp connections, some species being without 

 clamps until the formation of the basidium, while others have pre- 

 cise and regular clamp connections throughout the life cycle. He 

 discovered many irregularities in the behavior of mating types, 

 and this work was much extended later by Vandendries and Hanna. 

 Two mycelia of the same mating type often copulate and produce 

 clamps, due to an "illegitimate" mating ("Durchbrechingskopula- 

 tion"). Cultures grown from spore prints from a single fruiting 

 body may interact with great regularity according to the tetrapolar 

 scheme, but when a culture from a toadstool collected a few yards 

 away (whose spores likewise behave regularly inter se) are 

 tested, the two groups from the neighboring dungheaps are often 

 found to be completely inter-fertile. This has been interpreted as 

 due to multiple allelism of the genes A and B. Collections of my- 

 celia originating from different continents when cross mated often 

 reveal much sterility. 



BuUer discovered that a fully grown haploid AB mycelium in 

 contact with a haploid ab mycelium is invaded by ab nuclei and be- 

 comes a dicaryotic mycelium. Migration of ab nuclei through the 

 AB mycelium apparently accounts for this effect. The AB myceli- 

 um can also be dicaryotized by an Ab/aB dicaryon, although nei- 

 ther an Ab nor an aB mycelium can achieve this effect. Since only 

 an ab haplophase can dicaryotize the AB mycelium, this phenome- 

 non is puzzling. Many proposals have been made concerning the 

 mechanism by which the reaction occurs, but none is completely 

 satisfactory. My own preference is for an explanation which I have 

 not seen, published, but which Quintanhila proposed in the course 

 of a conversation: either the aB or the Ab nucleus in the dicar- 

 yon is converted into an ab nucleus by a directed mutation similar 

 to that which occurs in the transformation of pneumococcal types. 



Harder produced a dicaryotic mycelium by mating two vari- 

 ants of Schizophyllum commune, and operated on the dicaryon to 

 produce a haploid mycelium which contained the nucleus of one 

 variant in the mixed cytoplasm of the two variants. This is easily 

 achieved by cutting off the clamps of the penultimate cell before 

 it fuses with the ultimate cell and isolating the mononucleate ulti- 

 mate cell by cutting through the penultimate cell. He discovered 



