Manchester Memoirs, Vol. lix. (191 5), No. 8. 41 



distinguished from the outer xylem (b 2 ) between the 

 entering poles of -the leaf-traces and continuous with the 

 metaxylem of the leaf-traces. Outside the xylem comes 

 the parenchymatous xylem sheath (V), and outside that 

 again the phloem (d). A point of interest is the appear- 

 ance of the outermost tracheides of the outer xylem, 

 suggesting that they are the most recent addition to the 

 lignified elements of the stele. They suggest a secondary 

 addition from divisions taking place in the region of the 

 xylem sheath, and evidently correspond to the secondary 

 tracheides in a normal position mentioned and figured in 

 /. hystrix by Scott and Hill. 



In Photo 14, a complete section of the stele of this 

 plant at a lower level is shown, and at the same lower 

 magnification as the stele of the other plant in PL 2, 

 Photo 5. The difference in size of the primary stele of 

 the two plants is evident on comparing the photographs, 

 and also the difference in development of an anomalous 

 secondary zone. This is well marked in Photo 5, while 

 in Photo 14 the anomalous secondary growth is barely 

 indicated. The slight obliquity of the section is an ad- 

 vantage, for the plane of the section on the right of Photo 

 14 nearly follows that of an entering leaf-trace ; the extent 

 to which the xylem of the latter enters the stelar xylem 

 is thus well seen. On the left-hand side the continuity 

 between the phloem of the leaf-traces and the primary 

 phloem of the stem-stele is brought out by the develop- 

 ment of callus in the sieve-tubes. Internal to the phloem 

 the continuity of the parenchyma from the leaf-trace to 

 the xylcm-sheath of the stele can also be followed. 



These two points, the continuity of the phloem and 

 the deep attachment of the leaf-trace xylem, are of such 

 importance in the interpretation of the stele that it is 

 advisable to demonstrate them in longitudinal section also. 



