1900] SPOROPHYLLIS AND SPORANGIA OF ISOETES 337 
stem apex and a terminal cotyledon, and suggests a comparison 
with the embryo of Alisma for instance. The resemblance in 
form is undoubtedly very close, but we ought not to overlook 
some equally important differences. The entire absence of a 
suspensor in Isoetes, which has been brought forward as an 
objection to its close affinity with Lycopodium, militates quite 
as strongly against an affinity with monocotyledons; and the 
foot, which is particularly well developed in Isoetes, cannot 
be said to have any clear representative in monocotyledon 
embryos. 
In general habit Isoetes has been compared to some grasses, 
rushes, and the like; this is a mere external resemblance in one 
of the most adaptive features of plants, and not supported by 
internal and essential similarities. A similar objection can be 
raised to the comparison of the stelar regions of Isoetes and of 
such monocotyledons as Dracena. In the latter it is true there 
is a secondary thickening carried on by means of an extra 
stelar “cambium,” but this cambium merely adds parenchyma- 
tous tissue within which separate vascular bundles are organ- 
ized; there is nothing strictly comparable to the prismatic zone 
°r central xylem cylinder of Isoetes. Even were the likeness 
much closer than it is, the peculiar stem of Draczna, Yucca, 
etc., is so certainly a newly acquired, and not a primitive charac- 
ter, that it affords no sound reason for deriving monocotyledons 
through an Isoetes-like type. 
To one who has followed this discussion thus far it will be 
evident that in the writer’s opinion the balance of evidence is in 
favor of relating Isoetes to Lycopodium and Selaginella rather 
than to eusporangiate ferns. Of course the facts are not all in 
hand as yet, and new discoveries may materially affect the 
“spect of the case. The facts which the present investigations 
have brought to light certainly tend in the one direction. The 
ne of origin, development, position, and general characters = 
the ala the development of the leaf, and the nature : 
the - ‘ point to the correctness of including cesar amo 3 
ycopodiales; while the form of the. spermatozcids an 
