35 
itv and it "vvill fall from miv loaf which is not absolutolv horizontal and 
«/ ft/ n/ 
quiet; this is the case in respect to any leaf tlie surface of wliieh is 
unwettahle. * 
We have just seen that the surface tension of a drop nnist prevent its 
passing around a sharp edge; now, if drops run to a toothed margin, 
they must in part run over the sinuses. If the sinus were a curve with 
a radius equal to or greater than that of the drop, or if the radius were 
not very much less, the drop would have an area of contact greater than 
it would have in passing an entire margin, and so it would pass uiore 
readily. Sucli sinuses are found in Dipleris, but they are so placed that 
water^ to roach the uiajority of thorn, must run upliill. I liavo found siu^h 
sinuses in no otlier fern. If a drop runs to a sliarp sinus^ or to one 
much narrower than the diameter of the drop, then the sides of the slims 
will hold it up and make it run outward until the sinus widens or the 
ends of the teeth are reached. If the sinus widens sufficiently to allow 
the d]-(>p to run through, then even tliough the frond is quiet enough 
so as not to cause it to be shaken off when its contact is limited, and 
although it might return to the body of the frond while still touching 
both sides of the sinus, without its having to run uphill, nevertheless 
it is more than likely to leave the frond because of its impetus in falling 
through the sinus; this condition is easily demonstrated. If a drop 
runs out onto a tooth, it loses its opportunity to pass to the nether surface 
by diminishing its possible contact, just as it does if it runs on a caudate 
tip. In genera] water jnust run to the Leetli, rather than over a sinus, 
because its surface tension prevents its starting over an edge if it can 
run along it. Thus a toothed or cut margin in all parts of its periphery 
is provided with a water-removing structure such as caudate leaves have 
at the apex. I have demonstrated the inability of water to pass around 
a narrowly or sharply cut margin by experiments on various ferns. 
Among ferns with serrate margins are Nephrodium syrmaiicum^ 
Davalliu decurrenSj Dlplazium pallidum, D. 1G67, D, poIypodimdeSj 
Asplenium vulcanicum, A. macro pliyllnm, AUiyrium silvaticum, Ble- 
chnnm egregium_, sterile parts of Pteris ensifolia (a serrate fertile margin 
of Pteris is impossible), and the fertile frond of Drynariii rigidula. 
Beside being serrate (ratlier obtusely), DavaJlia dectirrcns has the seg- 
ments so close together that a drop will run on the upper surface from 
one to another.. In practice I have watched a drop run across eight 
segments without a particle passing through between them. Ferns with 
more deeply incised margin are PoIysHdnun, Nephrodium 1712, iV. in- 
termedium, X. Bordeniij Aspidium difforme, Davallia solida, Micro- 
lepia hirsuta, Lindsnya llavkei, Diplazivm WiUiamin, D. dolichosonim, 
D, meyeniuiiam, D. fruduosam, Asplenium raudatum, A. cuneaiuin, 
^diantutn diujdianuui, A. mindannoense, Schizo.'ifege. calornrpn and *S. 
pachysora. A very nnich larger proportion of terrestrial than of epi- 
phytic ferns have such margins; as epiphytes by virtue of tlieir position 
