Davis . — The Origin of the Archegonium . 489 
against desiccation demanded by the plant would sooner or 
later affect the details of structure. The plurilocular sporangia 
would respond to the conditions and become modified with 
other organs of the plant. Probably the first change would 
be the differentiation of an external protective tissue. This 
would require the sterilization of the outer layer of gamete 
mother-cells which would form a capsule enclosing the re- 
mainder of the tissue. The structure of such an organ is 
diagrammed in Fig. 21, b. An advance of this character would 
place the plurilocular sporangium in the same group of organs 
as the antheridium and archegonium. 
After such a modification of the plurilocular sporangium the 
more special peculiarities of the archegonium and antheridium 
would seem insignificant. The structure would of course all 
along have been under the influence of the principles that 
regulate the evolution of sex. The gametes might already 
have reached some degree of sexual differentiation ; or, if not, 
they would constantly tend in that direction ; and the results 
would eventually be heterogamy, with the continued specializa- 
tion of male and female organs. The female gametangium 
would retain its gametes as eggs, and the male would dis- 
charge its sperms under the proper conditions of moisture. 
The highest development would be attained in the female 
organ when, through the sterilization of the gamete mother- 
cells, all but one were sacrificed to the advantage of a 
specialized egg (see Fig. 21, c). 
And in this connexion we may again refer to Mr. Holferty’s 
unpublished observations upon the archegonium of Mosses. 
When the canal-cells form two or more rows at various levels 
in this structure, we have conditions exactly like those dia- 
grammed in Fig. 21, b and c. So these important stages in 
the evolution of the archegonium which we have assumed as 
necessary to the hypothesis are actually present, except of 
course that in the archegonium the canal-cells normally do not 
develop gametes \ But the evidence that the canal-cells are 
1 Since the above was written, W. C. Coker has described and figured (Botanical 
Gazette, XXXV, 136, 1903) an archegonium with two eggs, lying one above the 
