142 
The creeping stem of Pilularia grows from a single tetrahe- 
dral apical cell, from which three series of segments are cut off, as 
in most ferns. Two of these series give rise to the two rows of 
leaves, and from the third, roots only are formed. The stem 
branches freely, the branches arising close behind its apex. 
Leaves of two kinds are formed, fertile and sterile; the former 
differ from the latter simply in bearing a sporocarp. The foliar na- 
ture of the sporocarp has been inferred from analogy with the 
ferns, and also from a study of the position of the older sporocarps 
but the way in which it originates from the leaf was not known. 
Juranyi* states that in P. globulifera, the formation of the fruit be- 
gins, only after the leaf has reached a considerable size. My own 
observations on P. Americana do not confirm this. On the con- 
trary, the yonng fruit begins to develop almost as soon as the leaf 
can be recognized, and while it is still close to the apex of the 
stem, long before it is large enough to be seen with the naked eye. 
The young leaf, like the stem, grows from a tetrahedral apical 
cell. Growth at first is stronger upon the outer side, and in con- * 
sequence, even at a very early stage, the leaf is strongly coiled, 
as in all the homosporous Leptosporangiates. In the fertile 
leaves, however, before this curvature has become very pro- 
nounced, a protuberance may be noticed upon its inner face, not 
far above the base. (Fig. 1, M.) This originates from the growth 
of a single cell (x), which acts as an apical cell in the same way as 
that of the apex of the body of the leaf. This protuberance is the 
young sporocarp which at this stage is clearly seen to be simply 
a segment or branch of the fertile leaf. 
The young sporocarp enlarges rapidly after its formation and 
assumes the form of a blunt cone. Next, on the side turned to- 
ward the sterile segment of the leaf which bears it, a slight promi- 
-nence is noticed (Fig. 2, F.), and about the same time two similar 
lateral prominences are formed. As in the sterile segment growth 
is stronger on one side (here the side turned away from the sterile 
segment), and in consequence the sporocarp bends over toward 
the sterile segment of the leaf. The apex of the young sporocarp 
(Fig. 2, F.), together with the three prominences referred to, en- 
close a slightly depressed area which is top of the young sporo- 
#1... ¢, 
