1900 | SPOROPHYLLS AND SPORANGIA OF ISOETES 257 
apparently the innermost one, though that point is not made 
clear in the descriptions, becomes the megaspore mother cell.’ 
In certain other archesporial cells divisions take place in all 
planes, but more particularly in the anticlinal direction. The 
products of these latter cells give rise to the trabecule. Vines 
in his text-book gives nearly the same description, but says 
that the archesporial cell from which the megaspore mother cell 
arises undergoes but a single division. 
If the assertion be correct that certain archesporial cells 
develop only into trabeculz and certain others only into mother 
cells and tapetum, it is clear that there must be two categories 
of archesporial cells, one set destined to become sterile, the 
other to become fertile ; and these, although indistinguishable in 
appearance and size, are quite unlike in their mode of division 
and growth and in the ultimate fate of their derivatives. It is 
impossible, too, to escape the inference that the megaspore 
mother cells are already determined in position and number 
when the sporangium has got no further in its development than 
to the differentiation of an archesporium. Further, the spo- 
rangium must be regarded as compound, each fertile archesporial 
cell representing a separate sporangium, and each sterile one an 
imperfect wall. These conclusions, which I think are logical and 
necessary deductions from Goebel’s description, are all incon- 
sistent with the development of the sporangium as I have found 
it in /. echinospora. 
In order to bring out the points of contrast more clearly 
I will summarize them. I do not find any difference among 
the archesporial cells either in manner of development or of 
growth. I find no flattened tapetal cells overlying the megaspore 
mother cells. I find’no grounds whatever for the assertion that 
each archesporial cell follows an independent growth, or that 
each megaspore mother cell represents one archesporial cell. I 
do not even find a single definite hy podermal archesporium 
Which can stand as the starting point of the inferences above 
€numerated. On the other hand, I find the derivatives of all 
"See, however, SCHENCK’s Handbuch 3? 392. 
