206 BOTANICAL GAZETTE [MARCH 
surface is dry, it would appear that it is the dryness of the leaf 
surface rather than conditions of illumination that are responsible 
for the change of position of the chloroplasts. 
Conclusions 
The foregoing experiments have demonstrated that the filmy 
ferns may obtain water by any of three methods: root-absorption, 
leaf-absorption, and the absorption of atmospheric moisture by 
the leaves. By far the greatest mass of water intake is by leaf- 
absorption, root-absorption operating intermittently according 
to the wetness of the leaves. The high epiphytes are the only 
forms capable of availing themselves of atmospheric humidity, 
and the actual amounts of water thus obtained are small. The 
effect of a pronounced fall in humidity is to remove the water 
film from the leaves and to stop leaf-absorption; root-absorption 
is then taxed to a degree dependent on the lowness of the humidity 
and the duration of its lowness. Fig. 1 shows two drops in the 
humidity curve to below 70 per cent, neither of which lasted over 
2 hrs., and it is probable that this trace, showing 4 hrs. of humidity 
below 70 per cent in the week, is representative of the average 
conditions of the floor of the rain forest. : 
When the surface of a leaf remains dry in a moist atmosphere, 
many, or even nearly all, of the chloroplasts will be found on the 
lateral walls of the cells. The duration of dryness necessary t0 
bring this about varies from 3 or 4 hrs. in Trichomanes rigidum 
and other hygrophilous forms, to 8—r1o hrs. in Hymenophyllum 
polyanthos. In the more hygrophilous species the removal 1s 
accompanied by a curling of the leaf, which is more a function of 
the humidity of the atmosphere than of surface dryness. If leaves 
are dried and suddenly placed in an atmosphere of 7o per cent hu- 
midity or less, the curling will take place before the movement 0 
the chloroplasts. The movement appears to occur at times when 
there is no absorption of surface water taking place, but when thet 
is a maintenance of the turgidity of the leaf by the movement into 
the leaf of root-absorbed water. The shifting of the chloroplasts 
appears, in other words, to be such as to place them opposite the 
walls through which the entry of water is going on. 
