1898 | THE LEAF AND SPOROCARP OF PILULARIA 17 
confirmed by Campbell, and I believe it to be true, though I 
have not been able to follow out in detail this part of the devel- 
opment. 
Among the cells at the base of the sorus, where the first 
sporangia are formed, are a few cells which do not develop 
sporangia until much later, so that the sporangia in this region 
differ greatly in age, and hence in size (s 9, fig. 30). Inthe 
middle and upper portions of the sorus there seems to be much 
less disparity in the size of the sporangia, as all of the sporangial 
cells form sporangia at about the same time (fig. 29). From 
the similarity in distribution in the sorus of the sporangia first 
formed to that of the macrosporangia of the mature sorus, one 
is tempted to believe that these primary sporangia near the base 
of the sorus are the only ones that develop to macrosporangia, 
while the backward sporangia, including a few at the base and 
all those of the upper part of the sorus, give rise to micro- 
sporangia only, but this view could not be definitely confirmed. 
I can corroborate Campbell’s statement that no stalk cell is 
regularly formed in the development of the sporangia, and 
whether the cell sometimes seen at the base of the sporangial 
cell ( fig. 29) is the homologue of the stalk cell of the Poly- 
podiaceze seems open to question. 
We have seen that while the indusium which separates the 
sori of the laterally opposite pairs from each other is formed by 
the ventral outgrowth of sections II and V, that which separates 
the upper and lower sori of the same side must be derived 
principally from the sterile marginal cells. The presence of 
intercellular spaces along the median wall is noticed very early 
(i sc, figs. 25-27), and these finally run together to complete 
the separation of the indusia of the opposite sori. A similar 
splitting apart begins a little later between the upper and lower 
sori of the same side. 
The fact that these layers of tissue surrounding the individual 
sori are not originally separate is used by Goebel as evidence 
for the view that it is not an indusium morphologically, but it 
seems to me that, just as in Marsilia, the mode of development 
