Manchester Memoirs, Vol. xli. (1896), No. 1. 9 



Neither in transverse nor longitudinal sections have 

 any cellular elements been met with in the xylem, so that 

 the xylem may be said to be wholly vascular, so far as 

 observation has at present gone. 



Division of the Stele. 



The description of the stele given above does not 

 apply to all the preparations that have been examined. 

 In the majority a condition is met with which does not 

 appear to have presented itself to Williamson at the 

 time he dealt with this plant, and which shows the stele 

 in a state of division (Figs. 2, 3, 4, 5). As this appears 

 to be associated with the mode of branching of the plant, 

 and the formation of lateral members, it deserves to be 

 described with some detail. 



So far as has yet been seen, the division of the stele 

 takes place in one of two ways, being either (1) an equal 

 division, or (2) an unequal division. 



In equal division, the stele divides along a diameter 

 in such a way that the two halves have, from the first, 

 the same size, form, and appearance, and when the 

 process is completed we get two distinct steles of the 

 type already described. An early stage of the process 

 is well shown in No. no, where we have two semi- 

 circular masses of xylem, inclosed in a common zone 

 of phloem, and separated by a narrow band of thin- 

 walled parenchyma. This parenchyma cuts through the 

 xylem in such a way as to have the small groups of 

 elements, presumed to be protoxylem, abutting directly 

 upon it. As the two moieties of the stele become more 

 and more divergent, a centrifugal development of xylem 

 would seem to take place on the inner side of these 

 semi-circular masses until the circular contour is restored 

 in each, and we have the appearance seen in No. 105 

 (Fig. 2). Here we have two normal strands of xylem, 



