Knowledge of Rachiopteris cylindrical Will. 541 
the appearance of a sharply defined bundle sheath 1 (PL XXVI I, Fig. 4, e), the 
constituent elements of which alternate with those of the pericycle, and also 
with the cortical cells succeeding them. The distinctness of this darkened 
layer is very variable, and, particularly in the case of /3 stems, it is some¬ 
times so ill-defined that the stelar tissues appear to grade into those of the 
cortex without any reliable indication of a limiting layer. The dark colour 
of these cells seems to be due to the blackening of the contents, which must 
have been very dense. Sometimes the cells appear uniformly dark, as 
if the colouring belonged entirely to the walls ; in these cases there can have 
been little or no contraction of the cell contents. At other times the 
blackened contents have contracted away from the walls, locally or entirely ; 2 
Text-fig. 6. Portions of the middle cortex of a and /3 stems, showing the difference in the 
thickness of the cell-walls, and the appearances assumed by the contracted cell-contents, x 400. 
(a, from Q 101 ; / 3 , from Q 103, Cash collection.) 
while in still other cases the cells possess a pitted and reticulate appear¬ 
ance, suggesting uneven adhesion of the contents to the cell-wall, so that 
subsequent contraction has caused ruptures which now appear as spaces or 
pits. This appearance may be observed in longitudinal as well as in trans¬ 
verse section ; 3 whether it is natural, or due to a condition of petrifact, 4 
cannot of course be determined. 
1 Williamson (’ 78 ), p. 350 ; PI. 24, Fig. 80. 
2 Cf. Scott (’ 08 ), p. 329, Fig. 122. In this figure of Botryopteris hirsuta, contraction of the 
contents may be observed in the darkened cell-layer which ‘ may be the endodermis \ 
Kidston, R.: On a New Species of Dineuron and of Botryopteris from Pettycur, Fife. Trans. 
Roy. Soc. Edin., vol/46, Pt. II, 1909, p. 361. See p. 363 : ‘the endodermis (of B. antiqua) is 
clearly defined by its dark contents.’ 
8 The endodermis of the stem is exactly similar to that of the root, figured in PI. XXVII, Fig. 3 
and Text-figs. 12 and 13. 
4 Stopes, M. C.: Petrifactions of the earliest European Angiosperms. Phil. Trans. Roy. Soc., 
B, vol. 203, 1912, p. 75. See p. 94. 
