47 
1741, P- affine, P. Phymatodes, P. palmaturn, P. cdbido-squamatum, 
P. macrophyllum , P. heracleum, Dryostachyum and Photinopteris. 
White incrustations of lime are regularly found on these hydathodes on 
some species of Nephrolepis , P. albido-squamatum, and young fronds of 
Dryostachyum and Photinopteris and occasionally on various other ferns. 
There are other hyaline vein-tips, as in Asplenium subnormal e, which are 
not active hydathodes, though perhaps potential ones. 
V enation . — Except as it is modified by correlation with other structural ' 
peculiarities, such as the fineness of dissection of the frond, the venation 
in general is decidedly closer in species of arid than in those of humid 
habitats. - Thus, among plants of arid places, the distance between 
veinlets is :. 
Of N ephrodium eucullatum, 0.35 millimeter; N. aridum, 0.4 millimeter; Pteris 
opaca, 0.19 millimeter; P. longifolia, 0.5 millimeter; P. melcmocaulon, 0.5 mil- 
limeter; among plants of moister places; of N. ferox, 0.75 millimeter; N. Foxii, 
0.5 millimeter ; N. syrmaticum , 0.7 millimeter ; N. pteroides, 0.7 millimeter^ 
Lindsay a scandens, 0.7 millimeter; Syngramma, 1.5 millimeters; Diplazium pal- 
lidum, 1 millimeter ; Asplenium caudatum, 1 millimeter ; Soblopendrium pimiatum, 
2 millimeters; Stenochlcena ' subtrifoliata,, 2- millimeters; Pteris pluricaudata, 
0.7 millimeter; Pteris excelsa, 1 millimeter. 
Anastomosis of the veins makes the venation closer in effect, and as 
a general proposition, with many exceptions, ferns with anastomosing 
veins are more xerophytic in habitat than those with free veins. As 
illustrations on the largest scaled Goniopteris and Callipteris are dominant 
in the savanna- wood where Lastrcea and Diplazium do not occur, and 
Phymatodes and its offshoots have fifteen species in the high forest, but 
Eu-Polypodium is unrepresented. The frequent correlation between large 
size and ampleness of frond and reticulate venation is too obvious to need 
elaboration. 
Articulate stipe . — The articulation of the stipe to the rhizome, and of 
the pinnae or segments to the stipe, facilitate the reduction or removal of 
the leaf surface whenever it is necessary. It is thus an adaptation to life 
where plants must sometimes endure a more or less prolonged want of 
water. Like other adaptive characters, but in greater 1 measure than 
many, because it involves a deeper' specialization, it has a taxonomic 
value, as species, genera, and even larger groups have developed in 
constant adaptation to certain conditions. Under the conditions at San 
Eamon (and under tropical conditions in general), then, the character- 
istically epiphytic groups have articulate stipes; the characteristically 
terrestrial ones, nonarticulate stipes. Davalliece and Polypodies are 
typically epiphytic tribes with articulate stipes ; Asplenies, Aspidies and 
Pteridece, typically terrestrial tribes, without articulations. 
It is the exceptions to this general rule for the tribes which put this 
interpretation of articulations beyond any question. Among the Aspid- 
iece, we have at San Ramon a single epiphyte, N ephrodium 1712, and 
