56 LANG, Stele of the Shoot of hottes lacustris. 



PLATE IV. 



Photo 14. Slightly oblique transverse section of a stele without 

 evident secondary thickening, showing the general 

 structure, the continuity of primary phloem from leaf- 

 trace to stem and the deep insertion of the leaf-trace 

 xylem into the xylem of the stele. From the same 

 plant as the Photos in Plate III. ( x 67.) 



Photo 15. Continuity of primary phloem followed from stem 

 to leaf-trace in a stem without any secondary growth. 

 The sieve tubes are filled with callus. Cf. Photo 2. 



( * 130-) 



Photo 16. Similar continuity of phloem shown in afunctional 

 leaf-trace of the plant also shown in Photo 2. This 

 more highly magnified section shows the absence of 

 any secondary meristem and also the differentiation of 

 the stele in relation to the apical meristem. ( x 130.) 



Photo 1 7. Part of a longitudinal section of another plant show- 

 ing the deep insertion of the xylem of three leaf-traces 

 and the development of radially seiiated outer xylem 

 between them. ( x 130.) 



Photo 18. Tangential section of the outer xylem showing the 

 entering leaf-traces and the intervening tracheides. 

 ( x 130.) 



Photo 19. Portion of a transverse section of the stele of a plant 

 of /. setacea, where the first secondary tissues to be 

 developed are tracheides. The primary phloem is seen 

 internal to this anomalous secondary xylem which is 

 marked by the line from e. ( x 130.) 



