INTRODUCTION 



377 



These are spoken of as possessing bipolar sexuality in contrast to those 

 species with quadripolar sexuality such as described above. In a bipolar 

 species only one allelomorphic pair of incompatibility factors need be 

 assumed. 



Not infrequently a monocaryon mycelium may produce spore fruits 

 but in this case the basidia are less numerous and are either sterile or 

 give rise to but two, uninucleate basidiospores, both of the same sexual 

 phase as the parent mycelium. In Coprimis fimetarms Fr., Oort (1930) has 

 shown that two monocaryon mycelia may intermingle and together build 

 spore fruits when they represent phases alike genetically for one factor 

 and heterozygous for the other, e.g., Ab and AB. Such fruits are not 

 normal but may produce two kinds of two-spored basidia which are about 

 equally divided between the component phases, in this case Ab and AB. 

 It is apparent that no true sexual union has occured in such a case. That 

 this is more than a simple intermingling of separate monocaryon mycelia 

 is demonstrated by the fact that clamp connections may be formed, vary- 

 ing from incomplete or abnormal structures to those of perfectly normal 

 appearance. They vary from only occasional to frequent. The external 

 conditions appear to have considerable effect upon the number of clamp 

 connections produced. These unions do not arise in all incompatible com- 

 binations. Vandendries and Brodie (1933) showed that in Hypholoma 

 candolleanum (Fr.) Quelet, a quadripolar species, the mycelia to which 

 they ascribe the formula ab' when mated with a'b', or ab when mated 

 with a'b cause mutual partial inhibition of growth so that when growing 

 close together they are much smaller than when grown apart or in the 

 combination a'b X a'b'. It should be noted that the formulae ab, a'b, ab', 

 and a'b' correspond to AB, aB, Ab, and ab in the preceding portion of the 

 paragraph. The combination studied by Oort which produced a spore fruit 

 corresponds to the formula a'b X a'b'. Oort also found that such spore 

 fruits were not produced in certain other combinations. Quintanilha 

 (1935) made genetic and cytological studies of normal and "illegitimate" 

 crosses in Coprinus fimetarius and found that nuclear fusions may occur 

 in the basidia even in the latter type of cross. 



Vandendries and Brodie (1933) and Vandendries (1934) and Brodie 

 (1934, 1936) described what they termed "barrage sexuel." This had been 

 noted before by Oort (1930) and by Brunswik (1924) but not studied 

 intensively. This amounts to a mutual repulsion of the hyphae of some of 

 the incompatible matings. When two such cultures are established in the 

 surface of an agar medium the mycelia as they grow leave a gap between 

 the two colonies. This is especially marked in the aerial mycelium whose 

 hyphae show abrupt curvatures away when they approach the other 

 mycelium at a distance of 3 to 5 mm. These authors showed further that 

 the interposition of thin low plates of glass did not prevent this repulsion 



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