224 DR, A. C. SEWARD: 
lamina is strongly revolute the rolled segments resemble a miniature billet 
moulding, e.g. in G. dicarpa and G. alpina. The bud or partially unrolled 
crozier in the fork of a Gleichenia rachis is often accompanied by modified 
pinnules which serve a protective function: these are sometimes described 
as Aphlebie, a designation criticised by Goebel on the ground that they are 
merely special forms of pinnules. The Aphlebie may have the shape of 
ordinary segments, but they are occasionally larger and broader and may be 
bipinnate. In some species, c. g. Gleichenia linearis, the clusters of modified 
pinnules at the forks look like small Witches’ brooms: in G., pectinata they 
are broader and more deltoid than the normal pinnules and have a distinct 
type of venation. In this connexion the suggestion may be made that some 
of the Aphlebie characteristic of the rachises of certain Paleozoic pinnate 
fronds may be persistent protective structures homologous with those which 
cover the bud of a Gleichenia where the original dichotomous habit has not 
given place to the pinnate construction. 
The monotypic genus Platyzoma, an obvious xerophyte, bears tufts of 
simple or oceasionally forked leaves with very small segments associated with 
much reduced filiform leaves. The New Caledonian Stromatopteris has a 
horizontal rhizome giving off erect branches, repeatedly and irregularly 
forked, with fronds similar to those of Platyzoma but with rather larger 
segments. Gleichenia simples of the high Andes is exceptional in having 
unbranched fronds like those of juvenile plants of other species. 
The circular naked sori of Gleichenia usually have 2 to 5 sporangia, though 
in some species, e. g. Gleichenia pectinata, the sporangia are more numerous. 
In development the sori belong to the Simplices of Bower. In Platyzoma 
the stele is medullated. In Gleichenia it is often protostelic, but in 
Gr. pectinata it is solenostelic, Prof. Bower assigns the family to a position 
among the more primitive of the Filicales. The Dieranopteris section is 
generally regarded as more primitive than Hugleichenia. 
It remains to consider briefly the geographical distribution of the family. 
The subgenus Æugleichenia is confined to the Old World: Dicranopteris 
ranges from Japan to the Straits of Magellan and extends as far north in 
America as Mexico. The approximate limits of distribution are shown in 
Map A (PI. 16). Gleichenia occurs in the clearings of tropical forests, on the 
edge of jungles, on tropical alpine peaks, in the heath vegetation on the 
higher slopes of Ruwenzori, in Mexico, Patagonia, China, India, Australia, 
and elsewhere. The tangled fronds, their tall and slender rachises with out- 
stretched forking pinnæ, often in company with the genus /ipteris on the 
sun-exposed banks on the hill above Penang, present an impressive picture of 
tropical luxuriance. Malaya is one of many regions in the tropies and sub- 
tropics where the genus is rich in individuals and in species. Underwood 
describes Gleichenia thickets with “tunnels cut through them in which men 
could walk erect." Gleichenia flourishes in the rain forests of Mexico, in 
