46 Dr. W. C. Williamson on 



equal and unequal dichotomies. Of the equal ones I have 

 two sections from the same branch, in the lower of which 

 (C.N. 456) the inner or non-peridermal portion of the cortex 

 has a diameter of 71*5 mm. ; the Primary Xylem cylinder is 

 divided into two crescents which have not yet separated far 

 apart. In a second section made a little higher up in the 

 same branch, and with a slightly increased diameter of the 

 cortex, the two crescents are nearly an inch apart, and an 

 inward extension of the inner cortex already separates them. 

 In the British Museum at Cromwell Road is a much 

 larger section than C.N. 455, which is divided into two 

 virtually equal parts, each one of which will be as large 

 as the entire cortex of 455. This section is already 

 divided by a thin rudimentary cortical septum into two 

 incipient branches. The Primary Xylem in each of these 

 divisions has recovered its cylindrical form. We have 

 here a very large branch of the type of Wunschianum 

 undergoing an equal dichotomy. 



But we have examples of unequal dichotomy in the 

 same type. In my Memoir XIX. I have entered largely 

 into the subject of Halonial branches in relation to the 

 strobili which they supported or were destined to bear ; and 

 even in earlier Memoirs I demonstrated that the tracheidal 

 bundles, given off like huge leaf-traces from the Primary 

 Xylem, to the Halonial fruit-bearing tubercles, never 

 possessed a medulla. I have a very young example of one 

 of these fruit-bearing bundles divided into a consecutive 

 series of eight transverse sections. (C.N. 458 to 465). This 

 branch, like the young twig 428 — 432, has a solid tracheal 

 stele, but with the dimensions of C.N. 433. This Halonial 

 form is described and figured in my Memoir XII., the most 

 characteristic of my eight sections (C.N. 465) being repre- 

 sented in Fig. 21. The separation of small segments from 

 the periphery of the central stele is shown, each of such 

 segments going to one of the peripheral Halonial tubercles. 



