37 
devices which further obstruct the sinuses, is in itself a proof that cut 
margins are devices to prevent the passing of water to the nether surfaces. 
A mass of phanerogamic evidence for my thesis was accumulated by 
Anheisser, 15 who showed that in a great number of plants of various 
families, serrate or biserrate- margins and the restriction of stomata to 
the nether surface were concurrent phenomena. 
The epidermis. — Beside the excretion of a cuticle sufficiently waxy to 
be more or less unwettable, many ferns have outer walls the convexity 
of which is a strong factor in the same direction. These convex walls 
are sometimes confined to the nether surface, sometimes they are more 
convex in that situation. San Bamon ferns the epidermal walls of which 
are sufficiently convex to be difficult to wet are Stenosemia aurita, Davallia 
pallida , Microlepia hirsuta, Odontosoria retusa, Dennstaedtia Williamsi. 
D. cuneata, Asplenium subnormale, Adiantum philippense, A. diapha- 
num, A. mindwnaoense, Antropliyum reticulatum and Polypodium affine. 
Such an adaptation is naturally to be found chiefly in ferns growing in 
places where they are likely often to be wet; as a matter of fact, it is 
entirely confined to ferns growing in such places. 
It has already been remarked that half of the depth, of the cell of 
Adiantum diaphanum is made of the projections. Between walls which 
are convex to this extent, and trichomes, no line can be drawn. Dry 
trichomes, unicellular or p'luricellular, occur over the mesophyll of 
N ephr odium setigerum, N. immersum, N. canescens , N. aridum, N. 
cucullatum, N. pteroides, N. 1677, N. Bordenii, Nephrolepis hirsutula, 
Microlepia strigosa, M. Speluncce, Adiantum diaphanum, Niphobolus and 
Photinopteris. Very many species have them on the veins, the reason 
for this restriction being the mechanical one that their bases can be 
firmly anchored in the more solid walls to be found there. A better 
protection against wetting- than is produced by dry hairs is furnished 
by glandular ones such as are to be found on N ephrodium 17-12, N. 
setigerum, N, Foxii, N. immersum (f ew), N. canescens, N. aridum, N. 
cucullatum, N. pteroides (few), A 7 . 1685, N. Bordenii, and “MesochlaenaP 
These are of characteristic size, form and color in each species. 
The thickness of the outer walls of the epidermis has already been 
tabulated, which tabulation clearly brings out their relation to the gen- 
eral environment and the differences between epiphytes and terrestrial 
plants. These measurements are of the outer walls as they are apparently 
normally developed over parenchyma. However, many species have thin 
spots or pits around the periphery of each cell. These cells have their 
lateral walls wavy throughout their whole depth, or straight in the 
inner part but wav}r next to the outer wall. The thin spots in the outer 
wall are in the excurrent "angles or lobes. Ferns in which such pits are 
well developed are Didymochlaena, Dipteris, Humata het'erophylla, II. 
Anheisser, B,. : Ueber die aruncoide Blattspreite. Flora (1900), 87: 04. 
