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THE ROYAL SOCIETY OF CANADA 



primary wood present the transfusion tissue is connected with it. He 

 has observed, further, that in the higher forms where the centripetal 

 xylem has been replaced by secondary wood the attachment takes 

 place at the flanks of the latter. The degree of development to 

 which the wood has attained seems thus to be the deciding factor in 



Fig. 13. — Pintis strobus. 



Primordial, long., tang, at flanks of cf. — x 320. 



cf. — Centrifugal wood; cf. p. — Radial pitting on of; e. — Endo- 



dermis; p. — Parenchyma; R. — Medullary ray; tti and tto — Inner 



and outer transfusion tissue. 



determining where we shall find the attachment of transfusion tissue. 

 Worsdell and Bernard, however, laid especial emphasis on its origin 

 from and connection with primary wood and considered its attach- 

 ment with centrifugal xylem "a purely secondary result." Worsdell 

 states that the linkage with the primary wood is a definite indication 

 of "an extension" of centripetal xylem "towards the sides of the 

 bundle." Physiologically this may be possible, but all evidence from 

 the pine proves it none the less possible that transfusion tissue may be 

 as well a physiological extension of secondary wood. Moreover, the 

 term "extension," as used by Worsdell, postulates an active trans- 

 migration of cells, an idea which may have arisen as a result of observa- 

 tions on the transformations in animal tissues. However, in plant 

 cells transmigration is not known to take place. Again Bernard (2), 

 who goes a step further than Worsdell and claims the complete 

 identity of centripetal xylem with transfusion tissue, has failed to 



