of Lycopodium clavatum , L. 315 
the gametophyte recently obtained in both groups does not 
afford support to such a common origin. For the resem- 
blance between the prothallus of Lycopodium clavatum for 
instance and that of Botrychium virginianum x , which appears 
at first very striking, seems to be entirely homoplastic and to 
stand in relationship with the subterranean saprophytic life. 
It is in form and texture, position of the sexual organs, and 
the large foot of the embryo, that the likeness exists ; while 
the prothalli differ in symmetry, in the details of the sexual 
organs, in the spermatozoids, and in the embryology, points 
which when taken together must be regarded as of great 
weight. The resemblances between the prothalli of these 
two plants are of interest, as indicating how an appearance 
of affinity may follow from the modifications related to 
subterranean life of the prothallus, and afford an additional 
reason why the species of Lycopodium which possess similar 
saprophytic prothalli should not, on that evidence alone, be 
regarded as closely related and forming a sub-genus. 
The differences between the prothalli of the great groups 
of Vascular Cryptogams are indeed so striking, even when 
we confine the comparison to those which live in similar 
situations, as to be quite in accord with an independent 
origin of all those groups from Algal or Bryophytic forms. 
Within any one group, and especially within a narrow circle 
of affinity such as the genus Lycopodium , aid may doubtless 
be obtained from a consideration of the characters of the 
gametophyte. The critical attitude wffiich has been taken 
up in the preceding pages towards the immediate use of the 
gametophyte for the purpose of subdividing the genus Lyco- 
podium , is not intended to imply any doubt of the value 
of such characters, but to contribute to the separation of 
homoplastic from homogenetic resemblances, which must 
form the preliminary to any such use of the gametophyte in 
groups where it has become adapted to several different 
kinds of environment. 
Jeffreys, loc. cit. 
