58 THE ROYAL SOCIETY OF CANADA 



shaped end walls, often with indications of pits. On the walls in face 

 view are a number of very small bordered pits which show distinct 

 cross pores on focussing. This peculiar thin walled tissue above the 

 protoxylem was found in all sections examined, but its small bordered 

 pits could not always be made out. Moreover, there is further evi- 

 dence for considering this tissue of a tracheary character, since its walls 

 readily respond to lignin stains. From the fact that it occurs in a 

 position directly above the wood (Fig. 5) one may reasonably conclude 

 that it represents a vestigial centripetal xylem. 



In the wood fibres of Angiosperms there is, as is well known, an 

 interesting parallel to this modification of tracheary elements in the 

 pine. Here, on fibres which are recognized as transformed tracheids, 

 one meets with a gradual deterioration and elimination of pits. 



Worsdell in his observations on the foliage leaf of Pinus Pinaster 

 found "on the ventraP side of the protoxylem a group of thin walled 

 irregularly shaped rather small celled elements with lignified walls," 

 and "very small, but distinct bordered pits." The latter, in some 

 instances, he further records, were "almost obliterated" and, he adds, 

 "in a great many cases were entirely gone." He says, "it seems to me 

 that these tracheids represent the last lingering remnant of centripetal 

 xylem which is gradually becoming resolved into parenchymatous 

 elements." 



Jeffrey (6), however, doubts Worsdell's interpretation and con- 

 siders it "more highly probable such elongated elements are in reality 

 vestiges of the ancestral inner transfusion sheath." Even if we allow 

 Jeffrey's (6) claim that Prepinus is the "direct ancestor of Pinus" we 

 must acknowledge the doubtful character of this suggestion, for his 

 figures of the fossil (Figs. 3 and 4) show, between the protoxylem and 

 the inner transfusion zone, a very large development of centripetal 

 tracheids. His theory must necessarily entail the disappearance of 

 this "cryptogamic wood," and the consequent juxtaposition of the 

 inner sheath and the protoxylem. No evidence of such a process has 

 been presented. Further in Cordaites (Figs. 1 and 2), which is ad- 

 mitted by Jeffrey (6) to be "the ancestral stock from which the 

 Coniferales have been derived," the inner transfusional sheath does not 

 occur in the exact centripetal position, but merely attaches to the 

 flanks of the enormously developed centripetal xylem, which alone 

 occupies the region immediately above the protoxylem. Thus, in this 

 generally recognized ancestor of the group, one can find no elements of 

 the structure from which Jeffrey suggests that the thin walled tissue 

 has been derived. In consequence, the writer does not see any ground 



' Ventral, in the old sense, means directly above the protoxylem. 



