138 ARCHEGONIATES. 
by means of the theory of electrolytic dissociation of solutions, and 
with some success. As regards the spermatozoids of ferns, Buller has 
shown that in the case of some compounds, as certain salts of potas- 
sium and malic acid, the attraction is probably due to certain ions. It 
is not to be assumed, however, that a chemotactic stimulus may be 
given only by ions, for certain substances which are not dissociated 
have been found to exert a chemotactic stimulus. In this connection 
it is interesting to note that Pfeffer found that the spermatozoids of 
mosses are attracted by cane sugar, which does not attract the sperma- 
tozoids of ferns. 
Fic. 55.—Archegonium of Onoclea sensibilis.—(After Shaw.) 
A, vertical section through an open archegonium, probably within ten minutes after entrance of first 
spermatozoid; an unchanged spermatozoid is inside egg-nucleus. 
B, vertical section of venter of an archegonium containing spermatozoids, and a collapsed egg with a 
spermatozoid within nucleus; thirty minutes. 
Although malic acid exerts a strong chemotactic stimulus upon the 
spermatozoids of certain ferns, yet from the foregoing it is evident that 
the attraction by the mucilaginous substance extruded from the arche- 
gonium is not, of course, a decisive proof that malic acid compounds 
are present in that substance. 
Before the archegonium opens the egg-cell is concave on the upper 
side. The nucleus is also flattened or concave; it is in the resting 
stage and may contain one or more nucleoli. Shaw has observed that, 
in living sections, the egg swells as soon as the canal is cleared of 
its dissolving contents, and fills the venter. That part which was 
previously concave now forms the receptive spot. In fixed and stained 
preparations the author has found this same condition of the egg-cell 
