142 BOTANICAL GAZETTE [februasy 



young roots. The root tip differs in no observable respect from that 

 of Ceratozamia. 



In 



leaf traces alternate with the 



cotylcdonary strands, just above the cotyledonary node {fig. j). 

 Higher up (fig. 7), they close in, and together constitute the central 

 cylinder of the axis. Taking a generally vertical course, these trace 

 branch and anastomose until they reach a position so near to the 

 growing points of leaf and stem that the vascular tissue is still pro- 

 cambial. In this position, even before the procambial strands from 



margins 



manifest the phenomenon of girdling. 

 . At first the wood of the leaf traces is endarch. Fig. 8 represent- 

 a portion of a leaf-trace girdle, and fig. 9 a cross-section of two vertical 

 strands from the middle of the same leaf at the same level Figs. 10. 

 11 illustrate stages in the transition from the endarch to the mesarch 

 condition. The wood becomes exarch at a relatively low level in 

 some of the foliar strands, and there is considerable irregularity in 

 different traces in this respect. Fig. 12 is a drawing of one of the 



•4- _ _ /T\ • y» % 



fig 



The other 



traces of the same leaf retain, at this level, a few elements of centrifu- 

 gal xylem ; this strand is entirely destitute of them. Further-and 

 I have attempted to represent it diagrammatically— the wood in all 

 the traces of this petiole is more nearly exarch than in those of the 

 older leaf (/*), although the section of that leaf which is here repre- 

 sented is higher up in the petiole than that of the younger leaf. In spite 

 of such irregularities, however, the statement holds that the xylem B 

 entirely centrifugal near the base of both cotyledons and leaves, 



and 



porti 



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appearance and increase of centripetal xylem in the ascent of the 

 cotyledonary blade and leaf petiole. 



The section represented by fig. i 3 is very close to the leaf bases. 



Sh0ws the increa se in the number of bundles entering consecutive 

 leaves and also the meriphyte's gradual assumption of the fl arrange- 

 ment from the open arch of the early leaves. Transfusion tissue • 

 present in these traces. 



The strands are all collateral. Frequent branchings and app** 

 mat.ons occur, and real fusions- are common, most noticeably of 0*# 



IS 



