37 2 West. — A Contribution to the Study of the Marattiaceae. 
the stem, further complications resulting from the increasing importance 
and crowding of the compensating strands. Sooner or later, the gap 
above one compensating strand fails to be repaired until after the exit 
of the next, with the result that the internal vascular cylinder becomes 
broken up into a typical dictyostele, or, more strictly speaking, a ‘ per- 
forated’ dictyostele (cf. Tansley, 64, p. 65 ), since a few relatively small 
Text-fig. 6. i-v. Danaea alata , Sm. The diagrammatic figures illustrate in successive, but 
not consecutive, transverse sections the changes that occur in the internal vascular system of the 
rhizome of an adult plant at the transitional region (marked by a x in Fig. i A, Plate XXI). The 
smooth contours denote the endodermis, while the dotted contours mark the outer limits of the phloem. 
The shaded areas = xylem. m.c., mucilage canal. 
gaps, other than those formed by the departure of the compensating strands, 
occur in the internal cylinder. 
An interesting parallel may also be drawn between the leaf-traces 
and the compensating strands, which respectively pass through an onto- 
genetic series of stages starting with a simple single strand, passing through 
