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Transactions. 



groups corresponding to the leaf-bases. There is a very slight leaf-trace, 

 consisting of a few narrow phloem-like elements with no xylem. The 

 cortical cells are still thin-walled, but in some sections it is apparent 

 that the phloem and the other parenchymatous elements in the central 

 cylinder are beginning to show a slight thickening of their walls. Lastly, 

 in figs. 88 and 89, are shown the steles of the aerial stems of more 

 mature plants, in which there are five mesarch groups of xylem. In the 

 largest aerial stems of all there is a tendency for neighbouring groups of 

 xylem temporarily to join together, thus forming curving plates (fig. 89). 

 In these oldest stems the phloem and the " pith " elements are partly 



Fig. 85. — Transverse section of aerial stem of young plant. : 46. 



Fig. 86. — Transverse section of stele of aerial stem of y:>ung plant shown in 



fig. 87. X 140. 

 Fig. 87. — Transverse section of aerial stem of young plant. X 46. 



lignified, as has been described by Miss Sykes (1908, p. 70). In fig. 90 

 is shown a single xylem strand, illustrating its mesarch character and 

 the lignified nature of the surrounding elements. The leaf-trace is 

 collateral, and consists of two or three xylem elements and a group of 

 phloem (fig. 89). I must remark again that the plants of various ages 

 which I examined, and which are described above, all belonged to the 

 particular form of Tmesipteris referred to as T. lanceolata. In none of 

 the aerial stems of this form did I find the cortex collenchymatous, or 

 the presence of the brown deposit in its innermost cells. This is in con- 

 trast with what Miss Sykes states in her paper (1908, p. 70), for she found 



