The Anatomy and Relationships of the Gnetales. 
I. The Genus Ephedra . 1 
BY 
W. P. THOMPSON. 
1851 Exhibition Science Research Scholar , University of Toronto at Harvard University . 
With Plates XCIV-XCVII and two Figures in the Text. 
HE question of the true affinities of the Gnetales, alluring in itself and 
-1- yet hitherto so baffling, is being drawn into fresh prominence as 
morphologists turn to the great question of the origin of the Angiosperms. 
It is recognized that, aside from its own interest, a settlement of the 
Gnetalean affinities would mark a strategic advance in the attack on the 
ancestry of the dominant group of our modern seed-plants. Hitherto the 
chief attention of those who have added to our knowledge of the Gnetales 
has been focused on the reproductive structures, although even in this field 
much still remains to be done. The anatomical features have usually been 
dismissed with a bare reference to the occurrence of true vessels in the 
wood. There is accordingly great need of systematic study of the anatomy 
of the whole group, especially in accordance with the methods which have 
recently proven so fruitful of phylogenetic results when applied to the 
Conifers and lower Dicotyledones. 
The results of such an anatomical study of the most primitive member 
of the family, the genus Ephedra , are given in the present contribution. It 
is hoped soon to complete the study of the other genera. In studying 
Ephedra the writer has had material of several species, including E. altissima , 
californica , distachya , fragilis , Gerardiana , monostachya , trifurca , viridis , 
and vulgaris . There is little specific variation, so that all the species may 
be treated together and important differences mentioned under the features 
concerned. 
With regard to the history of the subject, it is contained chiefly in 
scattered references to individual features, particularly in general texts 
on anatomy. These will be mentioned as occasion arises. 
1 Contributions from the Phanerogamic Laboratory of Harvard University, No. 51. 
[Annals of Botany, Vol. XXVI. No. CIV. October, 1912.] 
