39 
our ferns. Here they may be equally distributed or they may be in 
streaks, or to a limited measure, in groups. They occur only over the 
parenchyma. . As the table shows, the number varies from 7 to 400 per 
square millimeter. As a general rule the number and size vary in 
opposite directions. 
In most ferns the outer walls of the guard cells are in the same plane 
as the outer walls of the epidermal cells. The guard cells are usually 
not very different from the epidermal cells in depth, but sometimes they 
are decidedly shallower. They are slightly elevated above the level of 
the surface in N ephrodium 1712, Microlepia Speluncce, Odontosoria retusa 
(by one-half their depth), Loxogramme conferta, Diplazium dolicho- 
sorum, Asplenium subnormals, Blechnum egregium, Pteris opaca, etc., 
Polypodium gracillimum, P. pediculatum, P. revolutum and P. affine. 
They are in effect immersed by outgrowths from the epidermal cells of 
Adiantum philippense and A. diaplianum, fill the bottom of pifs 10 /x deep 
in Dipteris, and occupy the middle of deeper pits in all our species of 
Niphobolus. 
In the majority of Polypodiacece, no ridge of exit can be detected. The 
exceptions at San Kamon are N ephrodium sparsum, Oleandra nitida , 
Humata heterophyllci , II. gaimardiana, II. parvula, Davallia solida, 
Lindsaya gracilis, L. blumeana, etc., Conio gramme fraxinea, Syngramma, 
Diplazium pallidum, D. meyenianum, Asplenium Phyllitidis, A. tenerum, 
A. macrophyllum, A. caudatum, A. cuneatum, A. affine, A. Belangeri, 
Scolopendrium schizocarpum, Stenochlcena , Pteris tripartita, Hymeno- 
lepis, Niphobolus, Prosaptia cryptocarpa, Polypodium ccespitosum, P. ce- 
lebicum, P. obliquatum, P. 171+1, P. dolichopterum ; P. incurvatum, P. 
Phymatodes, P. palmatum, P. angustatum, P. albido-squamatum, P. 
caudiforme, P , macrophyllum, Drynaria rigidula, D. quercifolia, Thaye- 
ria, Dryostachyum and Lomagramma. In most of these the ridge of 
exit is comparatively undeveloped; but in a few such as P. celebicum 
and P. Phymatodes the two ridges are about equal. Species with an 
especially strongly developed ridge of entry are Meniscium triphyllum, 
Davallia pallida, Microlepia pinnata, M. Speluncce, Odontosoria retusa, 
Dennstcedtia Williamsi, D. erythrorachis, Oallipteris esculenta, Diplazium 
.tenerum, Asplenium subnormale, A. resectum, Stenochlcena subtrifoliata, 
Pteris tripartita, Antrophyum latifolium, A. semicostatum, A. planta- 
gineum, A. reticulatum. Polypodium affine, P. macrophyllum and Chei- 
ropleuria bicuspis. In nearly all of these this ridge is prominent and 
aimed obliquely outward, as in Dennstcedtia punctilobula 1G ; but in 
Diplazium tenerum and in Antrophyum it is plane with the surface 
and in section remarkably like shears in appearance. In Stenochlcena 
subtrifoliata the ridge of entrance incloses a vestibule of considerable 
size. 
"Copeland: Mechanism of Stomata. Ann. of Bot. (1902) 16: 340. PI. IS. 
Figs. J+O, J,l. 
