io Hick, on Rachiopteris cylindrica, Will. 



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 particulars. 

 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 

 protoxylem. The smaller segment of xylem is composed 

 mainly of large tracheides, 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, 



