248 A TEXTBOOK OF THEORETICAL BOTANY 



a species is said to be a heterogamic homothallic one. One such example 

 is Absidia spinosa in which the gametangia are of different sizes. Here the 

 larger is regarded as equivalent to the female and the smaller to the male 

 gamete. It has been found possible to produce a hybrid between Absidia 

 spinosa and Mucor hiemalis, which has identical gametangia, that is, it is 

 homogamic but heterothallic. As a result of such a cross it has been 

 discovered that the ( - ) strain of Miicor hiemalis united with the larger 

 gametangium of Absidia spinosa, while the ( + ) strain of M. hiemalis united 

 with the smaller gametangium. It is therefore concluded that the ( + ) strain 

 of a heterothallic homogamic species is the female strain, while the ( - ) strain 

 is male. It may be mentioned that, as a result of biochemical tests, these 

 conclusions of Blakeslee have been substantiated (see Volume III). 



