356 Cutting.—On Androgynous Receptacles in Marchantia. 
polymorpha on germination always gave rise to thalli of the same sex as 
the parent plant, are quoted by Blakeslee ( 3 ) in support of his view that the 
sexual tendencies are separated at spore-formation in this species, and the 
experiments of Strasburger ( 19 ) on Sphaerocarpus , in which two female 
plants and two male plants came from each tetrad, point more strongly to 
a similar conclusion in this case. Also the experiments of E. and E. 
Marchal (14 and 15 ), in which regenerated portions of the gametophytes of 
certain dioecious mosses always gave rise to plants of the same sex as the 
experimental plants and a regenerated stalk of a sporogonium to monoecious 
plants, seem to prove this for certain of the mosses also. Both Harper ( 11 ) 
and Strasburger ( 19 ) have pointed out that this coincidence between sexual 
differentiation and the reduction-division is by no means a general one, 
so that even in the same genus the sexual differentiation may take place at 
different points in the life-history. 
In the higher plants the gametophyte is always unisexual, but the 
sporophyte often bears both mega- and microspores, and the sex of the 
plants arising from these is determined even before spore-formation. The 
interesting case of Salix, which is usually dioecious, but occasionally 
monoecious, shows that plants usually forming only one kind of spore— 
and this giving rise only to one kind of gametophyte—are capable, under 
certain unknown conditions, of forming both, and thus giving rise to both 
gametophytes. The power of forming both of these kinds of spore—and 
through them both kinds of gametophyte—was present in the plant, but the 
formation of one kind of spore was inhibited by some factor or factors. 
A similar case is to be seen in Lychnis dioica , in which the ordinary 
plants are strictly ‘ dioecious ’. The macrosporangiate form, when attacked 
by a smut fungus, forms microsporangia as a result of a stimulus caused by the 
fungus. A similar result has never been obtained by artificial stimulation, 
so that without the fungus we should not have known that the ‘ female ’ 
plants possessed the power of forming anthers. On several ordinary bisexual 
fern-prothallia we can inhibit the formation of either or both of the sexual 
organs, and the gametophyte of Equisetum , usually described as unisexual, 
can be made to bear either antheridia or archegonia or both by altering the 
external conditions ( 10 ). In many other cases it is possible that the plant 
contains the factors necessary for the formation of both sexual organs, but 
that one of these factors is obscured by some other internal or external 
condition. The case of Lychnis suggests that this factor, even if an external 
one, may be difficult to find or even to imitate when found. From this 
point of view it may be seen that many plants regarded as strictly unisexual 
may yet contain the factor necessary for the formation of the other sex. 
Any underlying phenomena that may exist in the inheritance of sex 
can only be arrived at by thoroughly investigating each separate case 
of sex-inheritance. The efforts to get at a general theory of the subject 
