MEANS OP REDUCING TRANSPIRATION. 27!) 



when we examine the salt-marsh vegetation. Most of the species of 

 that formation, even those which are wholly or partially submerged 

 at high tide, possess such structure. Xo plants of the North Carolina 

 strand are more conspicuously xerophytic in structure than Salicomia 

 herbacea and Spartina striata. That such structure is closely related 

 to the ability to take up NaCl in considerable quantities is proved by 

 the fact that certain species which do not naturally inhabit saline 

 soils, but which possess strongly developed modifications against 

 excessive transpiration, can absorb that salt in quantities that are 

 fatal to plants not so constituted. ' 



For this reason species belonging respectively to the sand strand 

 and to the salt marsh of Ocracoke Island are not distinguished in the 

 following enumeration of the means by which transpiration is reduced. 



1. Reduction of the transpiring surface, 



(a) Leaves small: Ilex vomitoria (smallest-leaved of our species of Ilex), Galac- 

 tia rolubili.s (unusually narrow-leaved form), Viiicetoxicum palustre, Tissa marina 

 (leaves hemicylindrieal), Monuiera monniera, Lippia nodijtora (leaves notably 

 smaller than in nonsaline soils), Sesuvium maritimum, etc. Most of the species 

 enumerated have small or narrow leaves as compared with the nearest related 

 inland forms. 



{(>) Leaves scale-like, their functions transferred to the stem, which is succu- 

 lent; stem succulents: Opuntia pes-corvi, Salicomia herbacea. 



(c) Leaves conduplicate or involute, especially in dry, sunny weather, so that 

 only the dorsal surface is exposed: All the grasses, and Cladium effusum, Fim- 

 bristylis spadicea, and other sedges. In the grasses this characteristic is corre- 

 lated with the position of the stomata, which lie at the bottom of furrows, espe- 

 cially on the unexposed ventral surface, and are further protected from air currents 

 by a network of hairs which line the walls. In Quercus Virginia net the leaf mar- 

 gins frequently become more or less revolute. 



(d) Leaves perfectly terete and in structure little differentiated from the stem: 

 Juncus roenwria n us. 



2. Position of the transpiring surface, leaves vertical or nearly so: Many of the 

 grasses and sedges, Typha, Juncus roemeruuuta, Triglochin striata, young leaves 

 of Yucca spp., Lippia nodiflora (sometimes), Viiicetoxicum palustre (leaves 

 reflexed), the Compositae. 



3. Development of protective modifications in the epidermis. 



(a) Thickened cuticle: Many species, notably the larger grass-like plants and 

 woody species with evergreen leaves. A shining upper leaf surface, as in I/ex 

 vomitoria, may be of use by reflecting some of the incident light rays, as has been 

 suggested by Wiesner. 



(b) Waxy covering: Panicum amarum, Uniola paniculata, Euphorbia pohj- 

 gonifolia, etc. This character is but slightly developed in the vegetation of Ocra- 

 coke Island. 



(c) Hairy covering: Oenothera humifusa and Teucrium nashii (hairs long, 

 simple); Quercus virgiuiana (stellate hairs on the dorsal surface only); Kosteletz- 

 kya virginica and Croton maritimus (hairs stehate, scale-like); Physalis viscosa 

 (hairs forked); Borrichiafrutescens (young leaves very densely covered with short 

 hairs, giving the surface a glistening appearance). Interesting hairs also occur 

 on other species, but not in sufficient numbers to serve as a protective covering 

 (except in the leaf furrows of certain G-ramineae). 



1 Schimper, Pfianzengeogr., p. 99. 



