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THE ROYAL SOCIETY OF CANADA 



in the modem form, to equal in length those at its flanks, or those 

 above it. However, this is not the case, and consequently this inter- 

 pretation of the origin of transfusion tissue can hardly be accepted, 

 without, at least, some reasonable explanation for the non-conformity 

 of cell length in the modern type. A physiological explanation seems 

 scarcely possible, since the uniform disposition of the chlorenchyma 

 around the stele would seem to favour the retention of a uniform 

 surrounding sheath. 



-«f- 



Fig. 7. — Pinus strohus. 

 Adult long. tang, at flank of centrifugal xylem — x 350. 

 cf. — Centrifugal xylem; e. — Endodermis; 

 tti and tt2. — Inner and outer layers of trans- 

 fusion tissue; p. — Parenchyma. 



The longitudinal radial section, (Fig. 8) shows the disposition of 

 tissues in the upper portion of the bundle. The presence of a large 

 parenchymatous cell interrupts the continuity of the two layers of 

 transfusion elements just within the endodermis. Immediately below 

 these, to the left, a much elongated parenchymatous cell is found, 

 followed abruptly by three rows of extremely thin walled elements just 

 above, i.e., to the right of the protoxylem. Four very small pits in 

 face view are discernible on the radial walls of these elements, while 

 on the square end wall shown, there was a structure suggestive of a 

 bordered pit. To the left, in Fig. 9, a tangential section, cut across the 

 pericycle just above the protoxylem, the nature of this tissue is more 

 clearly shown. The elements are much elongated and have variously 



