54 L. COCKAYNE 



is still xerophytic enough. Indeed there is no spot on the island 

 where, but for its presence, one would dream that the plant could 

 exist. 



During dry weather both Hymenophyllum sanguinolentum and 

 Trichomanes renijorme do protect themselves to some extent 

 through curling their fronds or rolling them tightly, as the case 

 may be. Moreover, T. renijorme, unlike most of the Hymeno- 

 phyllaceae, has its fronds four cells in thickness As for the rock 

 itself, it is extremely porous and must absorb a good deal of water 

 during the frequent and heavy rains, so that the air surrounding 

 such an apparently arid station may be much moister then might 

 be expected. But taking all the above into consideration, it 

 must be conceded, I think, that the fern is able to exist and 

 to tolerate strong desiccation through what Shreve designates 

 functional xerophily, 12 as in the case of various lichens, mosses 

 and liverworts. Such a property in the case of T. renijorme can 

 hardly be explained by any theory of evolution, but may rather 

 be considered a specific character of its protoplasm, since, as 

 aready explained, the species in question lives nowhere else except 

 under intense hygrophytic conditions. 



An interesting case of local discontinuous distribution is that 

 of Hymenophyllum Malingii, a fern also otherwise noteworthy. 

 This plant has narrow, more or less pendulous fronds 3 to 15 cm. 

 long. They are opaque and reddish or silvery in colour through a 

 dense covering of stellate hairs which quite hide the parenchyma. 

 This latter does not form a flat leaf-surface, but, as Giesenhagen 

 was the first to show, 13 consists of long cylindrical papillae which 

 surround the pinnately branched leaf nerves. The spaces between 

 these papillae are extremely narrow so that they form a richly 

 developed capillary system which is shut off from the surround- 

 ing air by the covering of stellate hairs. Thus the outer surfaces 

 of the chlorophyll-containing cells are in contact with water all 

 the time, as much as those of a submerged water plant, unless 

 during the very exceptional event of a protracted drought. 



12 Shreve, Forrest, Studies on Jamaican Hymenophyllaceae. Bot. Gaz., 51: 

 p. 209, 1911. 



13 Giesenhagen, K., Die Hymenophyllaceen. Flora, 73, p. 449, 1890. 



