210 Seward. — On Rachiopteris Williamsoni sp. nov. y 
composed of cells smaller in size and darker in colour than 
the subepidermal parenchymatous elements. Fig. i represents 
a small piece of this epidermal layer with the underlying larger 
and more oval parenchymatous cells. The hypodermal tissue 
is identical with that of Myeloxylon , and agrees most closely 
with the arrangement of sclerenchyma and parenchyma, typical 
of M. radiatum (Ren.) h Secretory canals are present in large 
numbers in this region of the petiole 2 , and, as frequently 
happens in such structures, they contain a central core of 
carbonized substance, which may probably be regarded as the 
fossilized remains of the products of secretion ; the black con- 
tents are often surrounded by a thin membrane, as previously 
described in the canals of Myeloxylon 3 . 
The fundamental parenchyma consists of fairly large thin- 
walled polygonal cells. Scattered throughout this parenchyma 
are a number of canals identical with those in the hypodermal 
tissue ; in some cases they are accompanied on one side by 
a group of stereome-elements, as in Fig. 3 ; in none of them 
do there appear to be any particularly well-marked tangentially 
elongated epithelial cells, such as are usually found in Myelo- 
xylon. One of these secretory receptacles, with its protective 
strand and fibres, has been figured by Williamson in Fig. 13, 
PI. Ill of the Myelopteris memoir 4 ; similar canals occur in 
some forms of Myeloxylon , as figured by Renault 5 . 
We must turn to the vascular bundles for the most im- 
portant distinctive features of the new species. The general 
arrangement is much the same as in Myeloxylon , and some of 
the peripheral and smaller bundles appear at first sight to 
conform to the collateral type characteristic of that genus. 
In some cases there is the same kind of space next to the 
xylem, which in Myeloxylon marks the position of disorganized 
phloem-elements ; a bundle of this type is shown in Fig. 4. 
The large space next to the protoxylem, and towards the 
1 Etude du genre Myelopteris . Mem. Acad. Sci. Paris, Vol. xxii. No. io. 1876, 
PI. I. 
2 Cf. Williamson’s Fig. 17, PI. IV, lo:. cit. 
3 Ann. Bot., Vol. vii. PI. II, Figs. 10 & 12 c. 
4 Phil. Trans, loc. cit. 5 Plates I, III, and IV. Renault, loc. cit. 
