THF FHYSIOI.OGV Ol' 1 TR Ill.l/A HON IN CII.IAII S 297 



between the two independent systems, four interacting mating types 

 may be obtained. This h\pothesis is presented for variety 1, P. bur- 

 Siiriij (a four-type variety) in Tal)le III. ^ designates tbc reaction be- 

 tween the two complementary substances, A and J, of one pair (the a 

 pair); simihirly i^ represents reaction between the members, B and b, 

 of the second pair C^ pair) of substances. 



TABLE III 



Proposed Explanation of Multiple Mating Types in 

 P. bursaria, Var. I 



Two independent pairs of specifically interacting substances, a and j8, are so 

 distributed that each mating type possesses one a substance (either A or a) and one 

 jS substance (either B or b). Mating occurs when A reacts with a (a reaction) and/or 

 B reacts with b {(3 reaction), a substances (.4, a) cannot react with jS substances {B, b). 



Mating" 

 Type A B C D 



AB Ah aB ah 



Note, a, substance A reacts with substance a; jS, substance B reacts with substance b. 

 ° Jennings' alphabetical system for designating mating types in P. bursaria is used here. 



This concept may be extended to include an eight-type variety 

 (variety II) by postulating three independent pairs of specifically 

 interacting substances. Each mating type should possess three mating- 

 type substances, one from each independent pair. By proper random 

 arrangement eight mating types should result. Any one of these types 

 should react with all the others, but not with itself, through specific 

 interaction between one or more pairs of substances. 



Support for this hypothesis is found in the mating behavior of 

 "adolescent" clones (Jennings, 1939a) and the intervarietal reactions 

 reported in F. bursaria (Jennings and Opitz, 1944). 



Exconjugant clones in P. bursaria pass through an "immature" 

 period of weeks or months during which they will not conjugate or 

 give mating reactions. This may be followed by a period of "adoles- 

 cence" during which the clones mate poorly and in some cases fail 



