88 
Margaret Benson 
given to Prof. Seward’s view if the Lycopodiales had not been 
regarded as the alternative to the Fern-Cycad alliance. 
Finally the writer wishes to express her full appreciation of the 
difficulties of the problem. They have however been probably ag¬ 
gravated by a too facile acceptance of an affinity between Conifer® 
and Gnetales. The latter group is regarded by the writer as a ves¬ 
tigial remainder of the Cycadophyta which instead of “magnifying 
the office” of the carpellary leaf (megasporophyll), as happened in 
Angiosperms, reduced it until it became obsolete. The Gnetales are 
probably a comparatively recent group, for there is no record of 
the Cycadophyta until the Triassic. As in the Cycadophyta we 
have in the Gnetales ample evidence of a micro-sporophyll and of 
a meriphyll type of foliage leaf, for both in Gnetum and Welwitschia 
we find reticulate venation and even a pinnate type in the cotyledon 
of the latter. On such grounds as these the Gnetales are entered in 
the accompanying diagram as surviving members of Cycadophyta. 
A warning note may be given with respect to the diagram. It 
is not intended to denote the relative dominance of the different 
groups in past epochs for there can be little doubt that the Stachyo- 
sperms were more abundant in the mesozoic times than even the 
Cycadophyta. The diagram and indeed the whole of this discussion 
arose in connection with an attempt to discuss the possibility of 
securing a logical sequence of Families of Vascular Plants for practical 
purposes. (See the “Note on a Numerical Sequence of Plant 
Families,” p. 90.) 
