-61- 
reaches the end of the group of archegonia (PI. VIII, figs. 4d, 6b, 6c). 
This fold of tissue remains lifted up from the thallus for a time, per- 
haps until after fertilization has taken place. Later these involucres 
are pressed tightly down upon the thallus underneath, securely en- 
closing the sporogonium. The number of archegonia formed seems 
to vary considerably, sometimes there are only nine or ten, and again 
there may be more than twenty (Fig. 29a). But ordinarily only one 
develops into a sporogonium, although twice I have found two full- 
grown sporogonia of equal size growing together under the same in- 
volucre. 
After fertilization the archegonia develop through the summer and 
autumn months into sporogonia which reach their full development by 
the last of October. These are composed of a foot, stalk (seta) and 
capsule, and remain hidden away under the tightly fitting involucres 
during the winter months until April, when the spores are ripe. 
Then the stalk which has remained short, suddenly elongates verti- 
cally to the height of an inch or more (Figs. 7a, 7b) the walls ^ of the 
capsule split vertically into four valves and the spores are shed. The 
foot is the basal portion of the stalk and in Pellia “is very distinct 
and forms a pointed conical cap whose edges overlap the base of the 
seta 2,” (Figs. 37, 38, 39, 43, 44). 
The study in preparation for this paper was undertaken with the 
purpose of finding out when the more important stages in the life 
history of Pellia epiphylla occurred. 
For this reason material has been collected in every month of the 
year, beginning in April when the spores are shed and the new plants 
begin their growth and continuing until the following April, when the 
life cycle has been completed. Collecting for this work was begun 
in 1908 and was continued during 1909 and 1910 as opportunity 
offered. Collections have been made from different localities about 
the city of Worcester, Mass., where Pellia epiphylla was to be found in 
fairly large amounts. For fixing agents several different chromacetic 
solutions were used with satisfactory results. The formula best suited 
to the earlier stages (those collected from April-July) was composed 
of 1 gram, chromic acid, 4 cc. glacial acetic acid, 100 cc. H3O. 
1 . “The growth of the seta after the spores are ripe is extremely rapid, but con- 
sists entirely in a simple elongation of the cells. Askenasi (Wachstum der Fruch- 
stiele von Pellia epiphylla. Bot. Zeit. 1874, p. 237) has investigated this in Pellia 
epiphylla and states that in three or four days the seta increases in length from about 
I mm. to in some cases as much as 80 mm., and that this extraordinary extension is 
at the expense of the starch which the outer cells of the young seta contain in great 
abundance, but which disappears completely during the elongation of the seta.” 
D. H. Campbell, 1. c. p. 93. 
2. D. H. Campbell, 1. c. p. 92. 
