io6 Dr. W. C. Williamson on 



ternal to its circle of leaves about "3 of an inch. In this 

 state (C.N. 428) its primary tracheal strand is wholly vascular, 

 devoid of any medulla, and about '125 in diameter. In 

 somewhat larger branches (C.N. 436) this primary strand is 

 enlarged to '16, but still without a medulla. In a yet larger 

 example (C.N. 434) this bundle has expanded into a primary 

 tracheal strand, in the centre of which is a medulla, "i in 

 diameter, surrounded by a tracheal cylinder with a diameter 

 of '2. It is only when the branches have advanced greatly 

 in size that any secondary tracheal strand makes its appear- 

 ance ; no trace of it exists in branches from which not only 

 the leaves but the sub-foliar prosenchymatous zone has dis- 

 appeared. I first find it beginning to develop in a branch 

 (C.N. 450), the entire diameter of which must have exceeded 

 six inches, whilst it attained its fullest expansion in stems 

 that were eighteen or more inches in diameter. In these 

 the secondary xylem strand attains a diameter of fully 

 27, in which examples the medulla has attained a width 

 of '5 and the primary tracheal cylinder of p. 



The cortex consisted of several layers. The inner- 

 most one is composed of a small-celled parenchyma, 

 which encloses numerous leaf-traces, as well as many 

 small vacant spaces which are transverse sections of 

 some vertically elongated cavities, conspicuous in longitu- 

 dinal sections. Externally to this is a broad zone of very 

 uniform parenchyma, composed of small cells passing 

 externally into another zone of uniform tissue but com- 

 posed of cells with thicker walls and of larger size. This is 

 enclosed in the usual zone of prosenchyma, which, in the 

 arborescent stems, has attained to a considerable thickness, 

 having increased with age. We only know the leaves in 

 their youngest state. They are imperfectly retained in the 

 section C.N. 434, but they are fairly represented in the 

 youngest twigs, C.N. 428 to 432. In 428 one leaf especially 

 exhibits the leaf-trace, the two lobes of the parichnos and 



