20 
The rains ceased in November. These results indicate — what indeed 
was reasonably to be anticipated, that during the rains and while their 
influence lasts, the air is moister away from the strand, but that with 
the advance of the dry season the savanna district becomes even drier 
than the strand. Occasional determinations showed this to be the case 
at all times except shortly after the rare showers throughout the succeed- 
ing months up to May. 
As compared with the strand, the savanna-wood is less suited for 
epiphytic vegetation, because : 
(a) During the driest season its air is even drier than that of the strand, thus 
necessitating most perfect structures in the ferns for the restriction of the loss 
of water. 
(b) The illumination is not in general as intense as it well may be for plants 
with exceedingly xerophytic structure. 
(c) Epiphytes here have no such supply of concentrated mineral food, as the 
strand plants have in the salt spray, which latter will allow an extremely limited 
transpiration to he sufficient to satisfy their needs. 
The conditions are less severe for terrestrial than for epiphytic vege- 
tation, but they still limit the development of ferns to a condition which 
is insignificant as compared with that found in the higher formations. 
While the atmospheric dryness stamps its character on all the vegetation 
of the coastal plain and amply justifies treating it as a single formation, 
there are great inequalities in the soil-moisture. Immediately back of 
the strand there are in several places considerable areas where the ground 
is wet throughout the severest droughts. In the wet season the air 
here must at all times be almost saturated. The two dominant genera 
in these low j ungles, Nephrodium and Callipteris, are alike in venation,' 
and so strikingly alike in aspect that sterile G. esculenta is constantly 
confused with Nephrodium by collectors. I have not yet been able to 
correlate the resemblance with the common environment. Several of 
these ferns have special devices to preserve the dryness of the repro- 
ductive structures; these will be taken up later. 
The drier parts of the savanna have ferns with smaller fronds and a 
distinctly more xerophytic structure, as appears for instance, in the 
thicker epidermal walls. Nephrodium' and Pteris are the dominant 
genera. Of Pteris, P. opaca, P. melanocaulpn and P. quadriaurita might 
almost as appropriately be included here as in the high forest; the two 
former are very local near the boundary between the two formations. 
The very large average number of stomata is a result of the large 
representation of Nephrodium and may or may not be correlated with 
the environment. 
THE HIGH FOREST. 
The high forest occupies the larger part of the land area within reach 
of San Eamon and has yielded me more ferns than any other formation. 
It includes all the forest in which epiphytes are a characteristic part of 
the vegetation and in which there is an evident difference between the 
