178 



MEGALOXYLEAE 



CH. 



much narrower and have the form of ordinary water-conducting 

 elements. On one side of the primary xylem in fig. 447 an oval 

 and more compact group of narrow and longer tracheids is seen 

 at It^; this is a leaf- trace about to enter the secondary-xylem 



x'^ n m 



Fig. 448. Megaloxylon Scotti. A, transverse section at the junction of the 

 primary and secondary tissues ; B, longitudinal section showing the inner 

 edge of the secondary xylem, x^, a leaf-trace, It, and the metaxylem, m. 



cylinder on its outward course. The same leaf -trace is shown 

 at It in fig. 446, B ; as it descends the trace becomes less distinct 

 and its elongated elements gradually merge into the general 

 mass of metaxylem. A portion of this leaf-trace is seen in fig. 



