62 THOMAS HICK, B.A., B.SC, A.L.S. 



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, separated by a band of phloem, and enclosed in a zone of the 

 same tissue. At a later stage, shown in No. 107, the two steles are 

 found to be completely formed, and are isolated from one another by 

 the intercalation of cortical tissue. 



In this mode of stelar division we obviously have a true dichotomy 

 of the same, and it can hardly be doubted that the process is associated 

 with a dichotomy of the axis itself. If this inference be correct, it will 

 follow that whatever be the nature of that axis, be it stem, petiole, or 

 other structure, it is characterised by a dichotomous mode of branching. 



In unequal division the stele divides into two portions, which from 

 the first, are conspicuously different from one another. Ultimately 

 they become converted into perfect steles ; but they are not alike, one 

 being of the normal type, and the other differing in important particu- 

 lars. An early stage of this mode of division is met with in No. 103 

 (Fig. 3), where a segment of the xylem, whose height is not more than 

 one-third of the diameter of the whole, is cut off from the rest by a 

 narrow band of delicate parenchyma, resembling that met with in equal 

 division. The dividing line passes through some of the smaller elements 

 which have been referred to as probably pro toxylem. The smaller seg- 

 ment of xylem is composed mainly of large ti'acheides, with only a few 

 smaller ones on the side turned towards the other segment. As the 

 process advances, the larger segment appears to receive an accession of 

 centrifugally-developed xylem on the inner side, by which the detached 

 segment is replaced, and the normal, circular form and appearance is 

 restored. The smaller segment seems to develop little or no xylem on 

 its inner side, and the typical form and appearance is not restored. 



Thus, in Nos. 101 and 102 (Figs. 5 and 4), where we find two 

 complete steles quite separated from one another, which have arisen 

 by unequal division, it is clear at a glance that the two strands of 

 xylem are very different from one another. The normal stele needs 

 no description. The other presents a xylem, semi-lunar in form, 

 with small elements on the flattened side and much larger ones 

 on the convex side. The number of preparations of this type 

 of stele is not large, and their phloem is not clear enough to 

 justify a definite statement; but two or three of them have raised 

 the suspicion that the phloem is mainly, if not entirely, restricted to 



