1900] SPOROPHYLLS AND SPORANGIA OF ISOETES 239 
Sections adjacent to that represented in fig. 37 show three or 
four hypodermal cells which have been cut off from the middle 
cells of the group and evidently belong to the same series. 
There is at no time a single complete hypodermal layer 
which may properly be termed an archesporium. For when the 
middle cells have just completed their periclinal divisions the 
lateral cells are still undivided, and by the time the lateral cells 
have undergone their first periclinal division the middle of the 
sporangium is at least three layers deep. A very good example 
of this is seen in fig. 42, which represents the side of quite a 
large sporangium. 
The growth of the sporangium is carried on most actively by 
the two or three outer layers of cells, as is evidenced by their 
large size and deeper staining, and the frequency with which 
they are found in karyokinesis. The divisions of the superficial 
layer are by no means limited to those in anticlinal planes, as 
is usually the case with the external cells of sporangia, but for 
a long time they continue to add to the inner mass by periclinal 
divisions, In the sporangium of which fig. 39 shows a section, 
as many as eight or ten of the external cells were in the act of 
periclinal division. Even in so old a sporangium as that shown 
in fig. 43 the same process is still in continuance. The cells 
marked with a cross have evidently been derived from the 
external layer. Though in older sporangia the additions so 
made go to form part of the sporangium wall, there can be no 
question that in the younger sporangia they add to the true 
Sporogenous tissue. The bearing of this fact upon the question 
of what: constitutes an archesporium will be considered further 
on. 
It seems necessary to digress at this point in order to make 
clear some features in which the preceding account differs 
from what has been recorded by previous observers. Both 
Hegelmaier (2) and Tschistiokoff (1) assert that the wall of the 
Sporangium is from the beginning (‘‘ von Anfang an gesondert”’) 
‘eparated from the inner complex, and emphasize with great 
distinctness the deep-seated origin of the sporogenous tissue. 
