330 BOTANICAL GAZETTE [MAY 
which being leptosporangiate cannot be closely related to 
Isoetes, the sporangia appear late in the history of the leaf. 
There is an enormous development of the midrib with its con- 
ductive tissues, and of the expanded pinne, before the sporan- 
gia are recognizable. Nothing is more striking, however, than 
the quickness with which in the Lycopodiales and Isoetes the 
rudiment of the sporangium follows the inception of the leaf, 
which when the sporangium first comes into view is no more than 
a mere papilla of undifferentiated tissue, without a sign of photo- 
syntactic or conductive tissue. 
Still more far-reaching is the agreement of Isoetes with the 
Lycopodiales in the character of the sporangium rudiment. 
Goebel. (1) in his celebrated paper of 1880-1 classified sporangia 
as leptosporangiate or eusporangiate according as they arise 
from single cells or from groups of cells. Though the two 
classes are connected by transitional forms, such for instance as 
the Osmundacee, in which the sporangia, though always classi- 
fied as leptosporangiate, do not arise strictly from single cells, 
the distinction has been approved by all later morphologists. 
The leptosporangiate plants make a well-defined and consistent 
group, but the eusporangiates comprise very diverse forms, 
including the several divisions of seed-plants, the Lycopodiales, 
the Equisetales, and part of the Filicales. If, however, we leave 
out accessories, and turn our attention entirely to the essential 
part of the sporangium, that is to the sporogenous tissue, We 
find a distinction which has the merit of leaving the Filicales 
an unbroken group, and of agreeing closely with what is required 
by a consideration of other characters. This distinction pertains 
to the origin of the archesporium. The spore-forming part of the 
sporangium of Isoetes and Lycopodiales can be traced back to 4 
number of cells placed transversely to the leaf, but of all other 
pteridophytes to a single cell. Is not this distinction as valid 25 
that which pertains to the origin of the whole sporangium f If 
so, it tends strongly to justify the inclusion of the Lycopodiales 
and Isoetes within a distinct group set apart from all other vas 
cular cryptogams. 
