Scott and Hill.—Structure of Isoetes Hystrix. 449 
A point on which stress is laid by Campbell is the presence of 
large, multiciliate spermatozoids in Isoetes , differing much from 
thesmalfbiciliate spermatozoids of Lycopodium and Selaginella , 
and resembling those of Ferns and Equisetaceae. This seems 
to us the one character in which Isoetes really agrees with 
the two latter classes, rather than with the Lycopodiales as 
at present known. We have no desire to minimize the impor¬ 
tance of this fact, but it cannot, as it seems to us, count for 
much against the aggregate of Lycopodinean characters. 
The embryology has also been much relied on by the 
advocates of Filicinean affinities, but the resemblance of the 
embryo of Isoetes to that of Ferns appears a remote one. In 
Ferns the cotyledon and stem arise from the epibasal half of 
the embryo, the root and foot from the hypobasal half, and 
all the organs are, as a rule, marked out extremely early. In 
Isoetes the root arises, with the cotyledon, from the epibasal 
half, while the lower portion produces the foot only. The 
stem is not one of the primary structures of the embryo at all, 
but appears quite late, between the cotyledon and the root. 
Botryckium 1 appears to resemble Isoetes in the origin of the 
root from the same half of the embryo as the stem ; it differs, 
however, from our genus, in the fact that the stem precedes 
the cotyledon in its development. It may be doubted whether 
the Isoetes-embryo, apart from the absence of a suspensor, 
does not agree quite as nearly with that of a Lycopodium as 
with the embryo of a Fern. The suspensor, however, is known 
to be a very inconstant feature in other groups of plants ; in 
some Leguminosae, for example, it is altogether absent, while 
in others it constitutes almost the whole of the embryo at an 
early stage. 
Taking the whole of the known characters of Isoetes , we see 
no reason to depart from the view, which for half a century 
has generally prevailed among botanists, that Isoetes is a true 
Lycopod. The recent ingenious attempts to connect the 
genus with the Filicales have not rested on any new dis¬ 
coveries, but have probably been unconsciously influenced by 
1 Jeffrey, 1897. 
