1911] SHREVE—JAMAICAN HYMENOPHYLLACEAE 209 
Summary 
. 1. The Hymenophyllaceae are most abundant in species and 
individuals at about 1525 m. altitude. 
2. The Jamaican species differ in their relation to moisture 
conditions from the most pronounced hygrophily to a relative’ 
degree of drought resistance. 
3. The differences of climate from floor to canopy in the rain 
forest determine the local distribution of the different types of 
Hymenophyllaceae. 
4. The low water loss from surface-dry leaves in a very moist 
atmosphere can be met by root-absorption in all but the most 
hygrophilous forms. 
5. The transpiration current moves when the leaves are wholly 
or partly surface-dry, but is at a standstill when the leaves are 
thoroughly wet. ee 
6. All but the most drought-resistant epiphytic species of 
Hymenophyllaceae are capable of living for considerable periods as 
submerged aquatics. 
7. The drought-resistant species are capable of absorbing 
atmospheric moisture when surface-dried, if kept in very moist 
8. Continued desiccation results in the loss of the water of the 
Sap cavity of all mature leaf cells, recovery depending on the 
duration of the desiccation. 
9. The relatively xerophilous epiphytic Hymenophyllaceae 
Owe their ability to resist drought to the capacity of the proto- 
Plasmic utricle of the leaf cells both to survive the replacing of the 
‘ap cavity by air and also to lose a rapidly diminishing amount 
of water on continued desiccation. 
to. The Hymenophyllaceae (structurally and physiologically 
“ very distinct group of ferns) have developed forms capable of 
towing in relatively dry situations through possession of an intra- 
cellular or functional xerophily, much less pronounced than that 
Possessed by many mosses and selaginellas, but like it in kind. 
TRE Desert LABORATORY 
Tucson, Arizona 
