68 THE ROYAL SOCIETY OF CANADA 



3. The centripetal xylem. 



Because of the lack of transition between it and the transfusion tissue, and 

 the impossibility of explaining the pericyclic distribution of the latter. 

 B. The evidence from Pinus strobus permits an interpretation of the origin of 

 transfusion tissue from parenchyma since it admits of: 



1. The variable pericyclic arrangement of elements in cotyledon, primordial 

 or adult leaf without necessarily demanding any explanation for the lack of 

 correlation with the fossil forms. 



2. The parenchymatous shape of the cells. 



3. The complete demarcation both in form and character of transfusion elements 

 from the cells of the centripetal xylem, 



4. The absence of radial arrangement at the connection with the secondary 

 wood. 



This work was done at the Botanical Laboratories of the Uni- 

 versity of Toronto under the supervision of Professor R. B. Thomson, 

 to whom the writer gratefully acknowledges her constant indebted- 

 ness for invaluable criticism and assistance. To Mr. H. B. Sifton, 

 M.A., the writer is also indebted for much valuable help. 



Bibliography 



1. De Bary— 



Vergleichende Anatomis der Vegetationsorgane der Phanerogamen und Fame, 

 Leipzig, 1877. 



2. Bernard — 



Le Bois centripète dans les feuilles des Conifères. Beihefte zum Botanischen 

 Centralblatt, p. 241, Bd. XVII, 1904. 



3. Coulter, J. M., and Chamberlain., C J. 



Morphology of Gymnosperms. University of Chicago Press, p. 237, 1910. 



4. Daguillon — 



Reserches morphologiques dans les feuilles des Conifères. Revue générale de 

 Botanique II (1890). 



5. Frank — 



Beitrzur Kenntn. d. Gefaszbundel (Bot. Zeit. Jhrg. XXII, p. 149, Leipzig, 

 1864). 



6. Jeffrey — 



On the structure of the Leaf in Cretaceous Pines. Annals of Botany. Vol. 22, 

 pp. 207-220, 1908. 



7. — 



The Anatomy of Woody Plants. University of Chicago Press, pp. 119-213, 

 1917. 



8. Karsten — 



Die Vegetationsorgane d. Palmen. (Abh. d. k. Adad. d. Wiss. zu Berlin, Séances 

 de 1847, Berlin, 1849.) 



9. LiGNIER — 



La nervation des Cycadées est dichotomique (Ass. fr. pour l'avancement des 

 Se. Congrès de Caen, 1894). 



