352 BOTANICAL GAZETTE (may 



here both wings contribute to the formation of a single branch 

 stele. Also procambium strands arise in the pith of the stem 

 opposite the leaf trace (tig. 5,^, 5); these develop a cambium 

 directed toward the center of the stem, which produces a small 

 amount of centripetal secondary wood which also contributes to the 

 vascular supply of the branch. But the greater part of the vascular 

 supply is furnished by the extra or accessory secondary xylem pro- 

 duced by the renewed activity of the cambium (fig. 5, C). In this 

 case, therefore, the branch connection consists of (1) accessory 

 secondary xylem, (2) adaxial extensions of the centrifugal xylem of 

 the leaf trace, and (3) a small mass of centripetal secondary xylem 

 originating within the pith of the leaf gap. 



One of the other branches shows almost exactly the same con- 

 nection, but the third branch shows a somewhat different situation. 

 In it the vascular supply is composed principally of accessory 

 secondary xylem; but a small mass of xylem appears in the peri- 

 cycle of the stem and contributes to the supply of the branch. 

 This pericyclic xylem is added to by a cambium directed toward 

 the phloem; hence we may speak of primary and secondary peri- 

 cyclic xylem, using the terms "primary" and "secondary" only to 

 indicate the presence or absence of a definite cambium. The 

 vascular supply of this branch, therefore, consists of (1) accessory 

 secondary xylem and (2) primary and secondary pericyclic xylem. 



Botrychium obliquum. — Four branching rhizomes of this species 

 were secured; three of these bore two branches each, and the other 

 had three branches. In all but one of these, the apical region had 

 been destroyed; but in this one case the rhizome had been injured 

 at the side below the apical region, but without destroying the 

 entire stele. In all the other cases, the branches developed near 

 the apical region. The vascular connection of the lowest of the 

 three branches mentioned above is shown by fig. 6. 



As shown by fig. 6, A, a very large development of accessory 

 secondary xylem occurs entirely around the stele before the leaf 

 trace separates; at the same level, a cambium has formed within 

 tlie pith opposite the leaf trace and has developed a considerable 

 mass of centripetal secondary xylem. The injury which occurred 

 at the side of the stele at a sli^hth' higher level has resulted in the 



