324 BOTANICAL GAZETTE [MAY 
represents the undeveloped sporangium. The sterilization of the 
sporangium does not affect the development of the velum, a 
fact which supports Hofmeister’s view of the primary separation 
of velum and sporangium. The occurrence of aborted sporangia 
on so many of the sterile leaves shows that all the leaves are 
potentially sporophylls, and suggests the probability that Isoetes 
has retained a more primitive form of the sporophyte than any 
other vascular plant. 
HOMOLOGY OF THE ARCHESPORIUM. 
The term “archesporium” was first employed by Goebel (1), 
who defined it as a cell, cell-row, or cell-plate, from which all 
the spore-producing cells are formed, and who concluded that in 
all sporangia the archesporium occupies a hypodermal position. 
Allusion has been made to the difficulty of accepting this con- 
clusion in such a case as that of Isoetes, but the difficulty is not 
peculiar to Isoetes. Bower has shown that in several pterido- 
phytes (Selaginella, Equisetum, Lycopodium) the archesporium 
is not delimited by the first periclinals of the outer layer. How 
shall we define the archesporium in cases where there is no 
single hypodermal layer from which the -whole mass of sporog- 
enous tissue is derived, and to which the term can be correctly 
applied as required by etymology and definition ? We must 
either modify our conception of the archesporium or abandon 
the term altogether as failing to express the facts. It appear 
to the writer that by changing our notion of the necessary posi- 
tion of an archesporium we could not only avoid this difficulty 
but would also be enabled to make a more consistent compartir 
son of the sporangia of seed-plants and pteridophytes than 18 
possible with the present nomenclature. 
It is pretty generally recognized that there is no true cpy 
dermis in pteridophytes. The so-called epidermis is physiolog!- 
cally but not morphologically equivalent to that of seed-plants, 
for a true epidermis is traceable to a primary layer of the embry? 
the dermatogen, which is distinctly present only in seed-plants: 
As the dermatogen is not represented in pteridophytes, unless it 
