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Relationships of the Gnetales . 
centripetal wood are quite like the conditions in Conifers, and quite unlike 
those in Cycads. The small amount of centripetal wood in the abnormal 
seedling leaves has its counterpart in several of the Conifers. 
Conclusions and Relationships. 
A complete discussion of the affinities of the Gnetales as indicated in 
an anatomical study is deferred until the other members of the group have 
been subjected to a similar study. Certain facts brought out in this 
investigation, however, may be emphasized here. 
As we have already noted, there is an increasing tendency at the 
present time to regard the Gnetales as derived from Cycadalean stock. 
The opinion has no doubt sprung from the conviction of many botanists 
that the Angiosperms have had the same origin, namely, from the Bennetti- 
tales, and that there is a real affinity between the Angiosperms and Gnetales. 
The fullest expression of this idea has been given by Arber and Parkin , 1 
whose conclusions have been reached almost entirely from a consideration 
of floral organization. They maintain that these two great groups have 
developed along parallel lines from a common ancestor which was in turn 
derived from forms like Bennettitales. Deferring the consideration of the 
Angiospermic relationship, let us see what bearing the results of the present 
study have on the idea of a Bennettitalean origin for the Gnetales. 
It may be stated at once that on the anatomical side there is very little 
evidence for connecting the Bennettitales with Ephedra , although this genus, 
being the most primitive of the Gnetales, is the one where the evidence 
ought to be found. The only notable feature of resemblance is the 
possession by both of multiseriate rays, but, as we have seen, those of 
Ephedra have undoubtedly been developed from a condition quite different 
from the Bennettitalean one, namely, from a uniseriate lignified condition. 
Therefore the only real anatomical point of resemblance proves valueless in 
establishing a connexion. 
On the other hand, there are a great many differences so vital as to 
make any real affinity extremely doubtful. Among those differences 
should be mentioned the course and arrangement of the primary bundles, 
the pitting of the tracheides, bars of Sanio, tertiary spirals, wood parenchyma, 
primitively lignified uniseriate rays, adult rays derived by fusion, double leaf- 
trace, absence of centripetal wood, and development of centrifugal wood in 
the leaf-trace. Thus almost every tissue presents grave obstacles to this 
view. All these differences constitute too great a mass of evidence to be 
overlooked, especially since there appear to be no anatomical resemblances 
on which to base a relationship. 
1 Studies in the Evolution of the Angiosperms : The Relationship of the Angiosperms to the 
Gnetales. Ann. Bot., 1908. 
4 C Q, 
