d 
280 PROCEEDINGS OF SOCIETIES. 
excluding the rhizomatous forms like Pteris, Polypodium, and Hymeno- 
hy 
and through which the parenchyma of the medulla is continuous with that of 
the stipes. In most Tree-ferns the medullary axis is lar 
group of Fern stems which I have already placed together under the name 
of Chelepteris 
invest the stem, from which, indeed, the generic designation was deriv l; 
while the structure of the stem itself has been overlooked. But this 1s 
bundles coming right out from the central parenchyma, where they existed 
as well-formed bundles, filling up more or less completely the medullary 
cavity. In one form (Zippea) the leaves are opposite, and the great p fe 
portion of the circumference of the stem is made up of the persistent an 
common vascular tissue: in ot : 
elements of the stem consists o 
appendages existing in the parenchymatous axis, and passing out int eye 
dently of any closed cylinder, The permanent elements of the eircumfer 
ence of the stems of ; 
1 3 i 
Dg. iro groups of » With differences | characterist 
those 
Ferns. i pit 
stems, comparable to those which distinguish the stems of mon 
ledons from of dicotyledons. But 
the caution I have alway? - 
