1906] BLAKESLEE—DIFFERENTIATION OF SEX 165 
the bryophytes has been understood to signify the existence of two 
kinds of gametophytes, male and female, and the condition in the 
sporophyte has been disregarded; while among the flowering plants 
the usage is changed and dioecism has had reference solely to the 
sporophyte. An inspection of the accompanying diagrams will show 
that a plant which is monoecious as regards its sporophyte may be 
either monoecious or dioecious as regards its gametophyte; and on 
the other hand a plant dioecious in its gametophyte stage may be 
either monoecious or dioecious in its sporophyte stage. The first 
case is illustrated by the ferns, which are all dioecious in the sporo- 
phyte though having both conditions in the gametophyte; and the 
second case is illustrated by the flowering plants, whose sporophytes 
are either monoecious or dioecious, but whose gametophytes are 
always dioecious. In flowering plants and in ferns, one of the two 
generations is characterized by only a single sexual condition, and 
attention has accordingly been directed to the other generation in 
which both sexual conditions are present. That this inaccuracy in 
the terminology has been allowed to stand so long unchallenged is 
probably due to the tacit assumption that the condition in the ferns 
is typical for all the archegoniates. Up to the present time, however, 
the sexual condition in the sporophyte of forms below the ferns has 
never, so far as the writer is aware, been a subject of investigation 
or even of discussion. | 
The terms hermaphroditic, monoecious, and dioecious have estab- 
lished themselves in use, and have their place as technical designa- 
tions in systematic botany of the flowering plants. As applied to 
the cryptogams, they have always been unsatisfactory, since the terms 
hermaphroditic and monoecious are used in descriptive botany to 
indicate whether the male and female sporophylls are produced in 
bisexual or unisexual flowers. In the cryptogams the terms lose 
their distinction with the passing out of use of the word flower. 
The greater or less local separation of the sexual organs or of the 
male and female sporophylls on a single individual is of little signifi- 
cance in comparison with the separation of the sexes on two entirely 
distinct individuals. Whether in Achlya, for example, the antheridia 
arise from the stalk which bears the oogonium as in A. racemosa, or 
are produced from separate special branches as in A. prolifera, is a 
