Section V, 1920 [5i| Trans. R.S.C. 



Vestigial Centripetal Xylem and Transfusion Tissue in the Leaf of 

 Pinus Strobus 



By Lilian V. Baker 



Presented by R. B. Thomson, B.A., F. R.S.C. 



(Read May Meeting, 1920) 



Transfusion elements, in the form of variously sculptured paren- 

 chyma shaped tracheids,^ constitute an intrastelar tissue of wide 

 occurrence in the leaves of the Gymnosperms. From the year 1847 

 since its first recorded observation by Karsten (8) the problem of the 

 origin, development and significance of transfusion tissue has greatly 

 interested a number of botanists. Of the earlier writers, Frank (5) was, 

 perhaps, the first to suggest its origin (1864). He considered the con- 

 nection of transfusion tissue with the centrifugal xylem of the fibro- 

 vascular bundle a definite indication of its derivation from secondary 



.c.p. 

 .?x. 



.t.S. 



Fig. 1. — Cordaites principalis. 

 [Transverse section of leaf bundle — Stopes 

 after Jeffrey (7.).] 

 cp. — Centripetal xylem. 

 i.s. — Inner transfusion sheath. 

 O.S. — Outer transfusion sheath, 

 px. — Protoxylem. 



* Coulter (3) divides the entire foliar pericycle into "two kinds of parenchy- 

 matous cells; (1) those without protoplasm and pitted and (2) those with protoplasm 

 and not pitted," and terms both groups of elements collectively, transfusion tissue. 

 All other authors, however, except, perhaps, Jeffrey (7), restrict their use of this 

 term to the former group of elements only, that is to the tracheary components of 

 the pfericycle. 



