Igtt} SHREVE—JAMAICAN HYMENOPHYLLACEAE 207 
When a gradual fall of humidity is experienced by surface-dry 
leaves, they assume withered shapes, and_air bubbles appear in the 
cavities. If isolated leaves in this state are placed in a moist 
chamber, they will resume an appearance of turgidity within a few 
hours, and while the bubbles are still present in the sap. This 
false resumption of turgidity is therefore no more than the absorp- 
tion of water vapor by the walls, and shows that the wetness of 
the walls rather than their distention by sap pressure is the cause 
of the turgidity of the leaves. The recovery of false turgidity is 
accompanied by considerable gains in weight, and these gains 
have already been shown to continue for several days. The absorp- 
tion of atmospheric moisture is not great enough to replace the 
air bubbles in the cells when they have once appeared. Leaves 
of Hymenophyllum polyanthos with bubbles in the older cells have 
been kept for 5 days in a nearly saturated atmosphere without an 
appreciable diminution in the size or number of bubbles. The 
cells at the tip of the leaf and the tips of the terminal pinnae, which 
are richer in protoplasm, were at no time deprived of water suffi- 
ciently to have bubbles, and doubtless drew upon the supplies of 
water in the older cells. 
The more hygrophilous species are not capable of withstanding 
4 considerable loss of water from their sap cavities; while both 
Hymenophyllum polyanthos and H. sericeum have been found capable 
of withstanding very great losses. The extreme extent to which 
the lumen of the cells of H. polyanthos may be replaced by air is 
shown diagrammatically in fig. 8. The exposure of a dry leaf to 
sunshine for 30 min. or to very dry air (60-40 per cent) for an 
hour will suffice to bring about this condition. If the duration of 
the condition is not more than 1-3 hrs., the leaf will recover on 
being wet up, the chloroplasts (at first misplaced) will gradually 
(perhaps only after several days) resume their normal position, and 
the leaf will survive. <A less degree of vacuolation of the leaf cells 
Can be withstood for a longer time, but repeated attempts have 
shown it impossible to obtain any very exact measure of the behavior 
of leaves in this respect. 
The Physiological behavior of the Hymenophyllaceae in respect 
to their capacity for enduring the loss of water from the sap vacuoles 
