Rickett.—Fertilization in Sphaerocarpos . 233 
finally by a contraction of the whole egg into a small body which lies 
free at the base of the venter. During this process of disintegration the 
distal concavity is usually more pronounced than previously, while at the 
other end the egg is quite sharply pointed. The remainder of the arche- 
gonium persists unchanged in appearance for a long time after the egg has 
disintegrated. 
The age of the archegonium may be judged approximately by the 
stage of development of the involucre. At the time of the maturity of 
the egg, the involucre is merely a cup around the base of the archegonium, 
extending sometimes to the base of the neck. Archegonia showing fertiliza¬ 
tion stages thirty-six hours after flooding are usually completely enclosed 
by the involucre, and after three days from the time of flooding the involucre 
extends a short distance beyond the end of the neck. The continued 
growth of the involucre is not dependent upon fertilization, although its 
form is considerably affected by the development of the sporophyte. 
A short distance behind the growing point archegonia containing eggs 
in the first stages of degeneration may be found, surrounded by involucres 
about thirty-six hours old (judging from the above account based upon 
cases of fertilization). From this time on the involucre enlarges rapidly, 
while the archegonium finally withers; so that the posterior part of the 
thallus is covered with the large cylindrical involucres, enclosing at their 
bases the remnants of unfertilized archegonia. The rate of growth of the 
involucre is so variable (compare Text-figs. 2 and 3 ) that estimates of 
its age based on its size, and consequently of the age of the archegonium 
based on that of the involucre, must be taken very cautiously. But it seems 
probable that the time during which an archegonium may be fertilized 
is limited to a period of from twenty-four to forty-eight hours after it reaches 
maturity, at which time the entrance of antherozoids is made more likely by 
the fact that the archegonium is not yet completely enclosed by the involucre. 
An archegonium with its involucre is represented in Text-fig. 2 . In 
this case the egg has been fertilized. Not all of the neck is shown, since 
its distal end curves, and portions of it appear in succeeding sections. 
Each archegonium is usually surrounded by its own involucre ; but on 
one plant I found two involucres each of which contained two archegonia. 
Two archegonia were found also which contained apparently two eggs each, 
side by side in the venter, and of about equal size. Several cases of similar 
abnormalities are to be found in the literature. Gayet (1897) reports that 
two superposed ventral canal cells are sometimes found in Sphaerocarpos. 
He found two ventral canal cells also in Marchantia , in this case side 
by side. Campbell (1896) reports the occurrence of two superposed ventral 
canal cells in Geothallus tuberosus. 
