39 
our ferns. Here tliey may be equally distrilmted or thoy may he in 
streaks, or to a limited measnro, in groups. They oceur only over the 
parenchyma. As the table shows, tlie number' varies from 7 to 100 per 
square millimeter. As a general rule the number and size vary in 
opposite directions. 
In most ferns the outer walls of the guard colls are in the same plane 
as the outer walls of the epidermal cells. The guard cells are usually 
not very different froiu the epidernuil cells in depth, but sometimes they 
are decidedly shallower. They are slightly elevated above the h\d of 
the surface in Nephrodium 1712, Mkrolepia Spcliincw, Odontosomi relusa 
(by one-half their depth), Loxoyratntne confcvta, Diplazium doliclio- 
sonuti, Asphnhini suhnonnalc, Blechnnm egregium, Pieris opara, etc., 
Polypodium grari/limvm, P. pedicvlntmn, P. revolalum and P. afjlne. 
They are in effect immersed by outgrowths from the epidermal cells of 
Adlantum pliilippense and .1. dlaphnuum, fill the bottom of pits 10 /a deep 
in Pipteiis, and occupy the middle of deeper pits in all our species of 
Niphoholus. 
In the majority of Polypodiaccos, no ridge of exit can be detected. The 
exceptions at San Ramon are Nephrodium spnrsiim, Oleandra nitida, 
llumata heterophylla, 11. gaimardiana, IL parvula, Davallui soUda, 
TAndmya gracilis, L. Uumeana, etc., Coniogramme frcuinca, Syngramma, 
Diplazium pallidum, D. meycnianam, Ai^pleninm Phyllitidi.% 4- irnrrum, 
A. macrophylhi m , A. caiidatnm, A. cuneatum, A. nffine, A. Belangeri, 
Scolopendrium schizocarpum, Sienochhena , Pteris tnpartita, IlymenO' 
lepis, Niphoholus, Prosaptia cnjpiocarpa, Polypodium cwspiloiiHm, P. ce- 
lehicum, P. oUiquaium, P. 1741, P. doUchoptcnim, P. incurvatum, P.. 
Phymatodcs, P. palmatum, P. angnstatum, P. alhido-sqiuimatum, P. 
caudiforme, P, macrophyllum, Drynaria rigidula, D. quercifoUa,. Thaye- 
rm, Dryoslachyum and Lomagrai/nHa. Tn most of these the ridge of 
exit is comparatively undeveloped ; but in a few such as P. celehicum 
and P. Phymatodes the two ridges are about Cijual. Species with an 
especially strongly developed ridge of entry are Mciilsrhiin friphylhim, 
DavaUla pallida^ Microlepia pinnata, 3/. t^polnncce, Odontomria retma, 
Dcnnstcvdfia Williamsi, D. eryihr orach is, Callipteris esculenia, Diplazium 
tenerum, Asplenium suhnormale, A, rescdum, Stenochlicna subtrifoliala, 
Pteris iripariita, Anirophyum laiifolium., A. semicostatum, A. pJnnfn- 
gincum, A, reiicnlntnm, Polypodium a^ne, P. macrophyllum and Chei- 
roplrjiria hicuspis. In nearly all of these this ridge is inoininent and 
aimed obliqufcly outward, as in VcnnshvdVui puncfiJohuJa''' ; but in 
Diplazium tenerum and in Anirophyum it is plane with the surface 
and in section remarkably like shears in appearance. In Stenochhma 
suhirifoliaia the ridge of entrance incloses a vestibule of considerable 
size. 
"Copeliuid: Moclianism of Stomata. Ann. of But. (10O2) 16: 340. /'/. /.?. 
