Manchester Memoirs, Vol. Ivi. (1912), No. \%. 7 



The departure of the leaf-trace from the stele and the 

 structure of the trace present considerable variety in 

 rhizomes of different size and age. From strong mesarch 

 steles a mesarch leaf-trace may be given off {Fig. 3A). 

 As this passes from the stele the centrifugal xylem of the 

 trace often extends round adaxially and meets to form a 

 complete ring ; this encloses the centripetal xylem and 

 some parenchyma. When the first division of the trace 

 is about to take place a structure results which is of 

 theoretical interest {Fig. 3B). In this a band of centrifugal 

 xylem extends across and separates the two halves of the 

 bundle ; within each half is some parenchyma and the 

 dying-out remains of the centripetal xylem, so that the 

 structure is still mesarch. This stage has been dis- 

 tinguished by Bertrand and Cornaille by the appropriate 

 name of the " clepsydroid trace," but has not been fully 

 described.^ 



In smaller rhizomes {^Fig. 2) the centripetal xylem 

 usually disappears from the inside of the trace before its 

 separation from the stele. The adaxial completion of the 

 centrifugal xylem, however, takes place as the endarch 

 trace departs {Fig. 2 a) and the clepsydroid stage follows 

 {Fig. 2B). In the case of very small rhizomes the depart- 

 ing trace may be almost as large as the stele remaining in 

 the stem, and owing to the completion of the ring of 

 xylem may present a general resemblance to the stem- 

 stele. While an adaxial completion of the xylem of the 

 leaf-trace is found in young plants as well as in larger 

 rhizomes, it does not always take place, and in plants of 

 all ages the departure of the trace and its dichotomy in 

 the cortex may proceed without the closure being effected. 



The structure of the stele and the mode of departure 



■* Travaux et Mciuoires de r Universit,! de Lille. Tome X., Mem. 

 No. 29, p. 179. 



