458 



R. K1DST0N AND D. T. GWYNNE-VAUGHAN ON 



The Departure of the Leaf-trace. 



The departure of the leaf-trace in Osmundites Kolbei is also of particular interest, 

 because the leaf-gap in the xylem ring is not formed immediately above the departure of 

 the xylem strand of the trace. On the contrary, as shown in text fig. 1, the inner 

 portion of the stem xylem is prolonged upwards for some distance beyond the point of 



Fig. 2. — Osmundites Kulbci. Diagram of a vertical section through the departure of a leaf-trace from the xylem ring, showing 

 that the xylem ring is not at once broken through. A pocket of parenchyma is formed, which gradually dies out below. 



departure of the leaf-xylem as a continuous plate of trachea}, separating the pith from 

 the soft tissues in the axil of the leaf-trace. The text fig. 2 is a radial longitudinal 

 section of the departing leaf-trace, and it also shows how it appears in transverse section 

 at different levels. From the transverse sections it is also seen that the plate of xylem 

 referred to above has a groove or furrow on its outer surface, which deepens as it passes 

 upwards until it breaks through the xylem plate and thus forms the actual leaf-gap (cf. 

 also PI. II., fig. 13). Following the leaf-trace downwards (figs. 10, 11, 12), it is seen that 

 the parenchyma of the xylem sheath in the axil of the leaf-trace is decurrent for some 



