54 THE ROYAL SOCIETY OF CANADA 



normal, and polyphyllous adult leaves. These were studied both in 

 transverse and longitudinal series. All drawings were made with the 

 camera lucida. Longitudinal figures have been so oriented that the 

 upper surface of the leaf bundle appears to the left, the lower to the 

 right of the page, respectively, while cross sections have been shown 

 in each instance with the xylem portion of the bundle towards the top. 

 The Adult Leaf. It was considered advisable to begin a study 

 of the adult leaf of Pinus strobus in order first to become acquainted 

 with the ultimate state of development to which the present day form 

 had attained. Whatever the morphological or anatomical structures 

 which characterized the ancestor of the group, it is natural to expect 

 the condition here to register the greatest degree of departure there- 

 from. 



Fig. 5. — Pinus strobus. 

 Transverse section of adult leaf bundle at centre — x 300.) 

 b. — Bast; cf. — Centrifugal xylem; e. — Endodermis; p. — Paren- 

 chyma; px. — Protoxylem; tt. — transfusion tissue; v.cp. — Vestigial 

 centripetal xylem. 



Turning first to a consideration of the adult stele, in transverse 

 section (Fig. 5) one finds a general tendency on the part of the trans- 

 fusion tissue to resolve itself, above and below the bundle, into two 

 irregular layers, interpersed with parenchyma while laterally by 

 additional transfusion elements it comes into direct continuity with 

 the secondary wood. Radial longitudinal sections prove the outer 

 layer of tracheary tissue immediately below the bundle to be com- 

 posed of short and comparatively broad elements, while the inner row 

 isobserved to consist of longer and relatively narrower cells (Fig. 6) . The 



