COMPARATIVE ANATOMY 



333 



number from three to eight, as slightly projecting groups of small spiral 

 tracheides. The condition thus attained is very similar to that seen in 

 the simpler types of Lycopodiitm : or a better comparison may perhaps 



C 



A 



st 



FIG. 174. 



Lcpidodendron Harcourtii. A= transverse section of stem; st = stele; o.c outer 

 cortex ; both here and in the outer cortex the leaf-traces are shown about natural size. 

 2> = stele of same ; / = pith, hollow in the middle ; .r = xylem-ring ; /_r = protoxylem-points. 

 The leaf-traces join the stele between them ; l.t = leaf-trace bundles, of which the outer, 

 /.?', show xylem and phloem; z'.c = inner cortex, x 7. (From Scott's Studies in Fossil 

 Botany.) 



be drawn with certain stems of Lepidodendron. The presence of central 

 and peripheral protoxylem in different parts of the same shoot should be 

 a warning against too great reliance upon such characters ; it may, perhaps, 

 indicate that the central position was the more primitive, as is believed 

 by some on general comparative grounds. At the same time it is of 



