No. 461.] AFFINITIES OF EQUISETUM. 279 
there is decidedly more resemblance between the gametophyte 
of Equisetum and that of the lower ferns than there is between 
it and any species of Lycopodium. 
THE EMBRYO. 
According to Sadebeck,! who has made a special study of the 
embryo of Equisetum, the primary or basal wall of the embryo, 
which is transverse, divides the embryo into an upper or epibasal 
cell, and a lower or hypobasal one. From the epibasal cell is 
derived the apex of the shoot ; from the hypobasal one the foot 
and the primary root. My own studies upon Zguisetum_ tel. 
mateta, although not complete, confirm Sadebeck's statement. 
Jeffrey? thinks it doubtful whether the root in Zguisetum Ate- 
male and Equisetum limosum originates from the hypobasal 
region of the embryo, but to judge from his figures 7, 8, it is 
by no means certain that his interpretation is correct. While 
comparing the embryo of Equisetum with that of Lycopodium, 
in which all of the organs of the embryo arise from the epibasal 
half, he fully recognizes the fact of the presence of the sus- 
pensor in the lycopods, and its absence in Equisetum. Even 
if his assumption of the epibasal origin of the root were correct, 
it could more aptly be compared with the embryo of Botrychium, 
where he has shown? that both root and shoot are of epibasal 
origin, and moreover, the cotyledon develops secondarily from 
the shoot as the first foliar sheath does in Equisetum. 
THE MATURE SPOROPHYTE. 
The sporophyte of Equisetum, as is well known, differs 
‘widely in its general structure from either the ferns or lyco- 
pods. The structural type as it exists in the living horsetails is 
evidently a very ancient one, and the oldest fossils belonging to 
the Equisetales are not essentially different in their structure 
from the living species. 
! Bot. Zeit., 1877. 
2 Loc. cit., p. 169. 
3 The Gametophyte of Botrychium. Proc. Canad. Institute, vol. 5, 1898. 
