Knowledge of Rachiopteris cylindrica, Will . 547 
smaller than the parent stems, having a diameter of about 1*3 mm. (PL 
XXVI, Fig. 7). The xylem strand, like that of the stem, is much reduced, 
measuring only about 0-15 mm. x 0-3 mm. Below the level of petiolar 
separation the trace is usually semilunar in transverse section (PI. XXVI, 
Text-fig. ii. a , transverse section of a petiolar bundle, showing the adaxial distribution of 
the smaller elements, which seem to lie in two shallow grooves. At m there is an appearance similar 
to that figured in PI. XXVII, Fig. 1, suggesting the breaking down of adaxial metaxylem elements. 
Note the general shape of the petiolar bundle, and the slight depression of the posterior margin, 
x 230. (From slide 1862, Williamson collect.) b, the anterior margin of a similar petiolar bundle, 
in which the protoxylem seems to be aggregated into two blunt points. At m the cells appear 
somewhat broken down. x 400. (From slide 1861, Williamson collect.) N.B. It is impossible 
definitely to refer this petiole to R. cylindrica , although its appearance suggests that it belongs to 
this species. 
Fig. 9, It; PI. XXVII, Fig. a ); at a somewhat higher level it is bluntly 
triangular, the protoxylem being concentrated at the apex of the triangle. 
The monarch condition is maintained in /3 petioles, and no adaxial 
metaxylem is formed (PI. XXVI, Figs. 7 and 9 ; PI. XXVII, Fig. 2 ; 
Text-fig. 8), so that the protoxylem is always external. 
The cortex of (3 petioles is wide in proportion to the size of the xylem 
