pia RonF. 
VOLUME XLII NUMBER 3 
BOTANICAL Gaver 
SEPTEMBER, 1906 
DIFFERENTIATION OF SEX IN THALLUS GAMETO- 
PHYTE AND SPOROPHYTE.* 
ALBERT FRANCIS BLAKESLEE 
(WITH PLATE VI AND THREE FIGURES) 
IN a recent article (5) the writer has given a somewhat detailed 
account of zvygospore germinations in certain species of the Mucorineae. 
The purpose of the present paper is to point out the bearing which 
the investigations already made in this group may have upon the 
questions of sexuality in other forms. Some of the problems for 
research which the facts observed in the mucors would suggest will 
be indicated, and it is hoped that in forms in which an alternation of 
generations occurs the distinction between differentiation of sex in 
the gametophyte and that in the sporophyte will be more clearly 
drawn than has been done previously. The various grades of differ- 
entiation in the gametes themselves or in the gametophyte and 
sporophyte will not be discussed. The subject for consideration 
rather will be the sexual condition in the plant as a whole. 
According to the sexual character of their thalli, the species of 
the Mucorineae have been divided (2-6) into two main groups, 
homothallic and heterothallic—designations which correspond in the 
main to the terms hermaphroditic and dioecious respectively. In a_ 
homothallic species the thalli are all sexually equivalent, while in a 
heterothallic species the thalli are of two different kinds, which have 
been provisionally designated by the symbols (+) and (—). The 
sexual character of the (+) and (—) mycelia remains constant when 
* This paper was written while working under a grant as research assistant of 
the Carnegie Institution, to whom the writer wishes to express his indebtedness for 
the opportunities for research afforded him. 
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