go BOTANICAL GAZETTE [JANUARY 
as a demonstration or even as evidence of genetic connection 
between them; it is rather to be used as a remarkable illustration 
of development by different plants of the same highly specialized 
structure. It is to be compared with the independent evolution in 
lycopods, horsetails, and ferns of similar seedlike structures. To 
what extent this applies to other points of resemblance between 
Gnetales and angiosperms is reserved for future discussion. 
Summary 
1. The vessel of Guetum with the single large perforation in its 
end wall has been evolved by the enlargement and fusion of several 
haphazardly arranged bordered pits. 
2. The vessel of angiosperms with the similar single large 
perforation has been evolved from the type with many long, narrow, 
scalariform perforations. 
3. On account of the entirely different courses of evolution by 
which they were produced, there can be no genetic connection 
between the vessels of the two groups. They furnish a remarkable 
illustration of independent development of similar structures. 
4. The possession of vessels by both angiosperms and Gnetales 
cannot be used as an argument in favor of the derivation of angio- 
sperms from Gnetales or of both from common ancestors. 
UNIVERSITY OF SASKATCHEWAN 
SASKATOON, SASK. 
LITERATURE CITED 
1. Boopte L. A., and Worspett, W. C., Some points in the anatomy of 
Casuarinaceae and Gnetaceae. Ann. Botany 8:231-264. 1894. 
2. Dutute, A. V., The anatomy of Gnetum africanum. Ann. Botany 27:593- 
602. 1912. 
3. JEFFREY, E. C., and Coreg, R. D. " guspsiracccas investigations on the genus 
Drimys. Ann. ‘Potty 30:359-369. I 
4. THompson, W. P., Anatomy and peroneal Cs of Gnetales I. Ephedra. 
Ann. Botany 27: joie. IQI2. 
, Morphology and affinities of Gnetum. Amer. Jour. Bot. 3:135-184- 
S. 
Tg16. 
6. THompson, W. P., and Barzey, I. W., Are Tetracentron, Trochodendron, and 
Drimys soectilicel or primitive types? Mem. N.Y. Bot. Gard. 6: 1916. 
