MEANS OF REDUCING TRANSPIRATION. 279 



when we examiue the siill-inarsh vegetat iuii. Must of the species of 

 tliat formation, even those wliieh are wliolly or partially submerj^ed 

 at high tide, possess siieh structure. No plants of th<' North Carolina 

 strand are more conspicuously xerophytie in structure than Salirornid 

 lierhacea and Spartina stride. That such structure is closely related 

 to the ability to take up NaCl in considerable (iuantities is i)nn cd \)y 

 the fact that certain species which do not naturally inliahit saline 

 soils, but wdiich possess strongly developed modifications airaiust 

 excessive transpiration, can absorb that salt in ([uautilics ihai are 

 fatal to plants not so constituted. ^ 



For this reason species belonging respectively to the saml si rand 

 and to the salt marsh of Ocracoke Island are not distinguished in lh<3 

 following enumeration of the means by which transpiration is i«'<l nc-d. 



1. Reduction of the transpiring surface. 



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

 tia rolubiUs (unusually narrow-leaved form.) ,Vincetoxicinii palast re, Tis.sd marina 

 (leaves liemicylindrical), Monniera monniera, Lippia xodijiora (leaves notably 

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

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

 inland forms. 



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

 lent; stem succulents: Opuntia pes-eorvi, Saliconiia licrbacea. 



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

 only the dorsal surface is exposed: All the grasses, and Cladiioa effusnm, Fim- 

 bristi/Us s2Jadice((, and other sedges. In the f^rasses 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 Quercua viryiniana the leaf mar- 

 gins frequently become more or less revolute. 



Ul) Leaves iDerfectly terete and in structure little ditferentiated from the stem: 

 Juncus roemeria n us, 



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

 grasses and sedges, Tijplia, Juncus roemeria mis, Friijloehin striata, yonui^ leaves 

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

 reflexed) , the Compositae. 



'S. 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 Ih\c 

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

 suggested by Wiesner. 



(b) Waxy covering: Panicum amarum, Uniola panicidata, Euphorbia poly- 

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

 coke Island. 



((') Hairy covering: Oenothera hnmifusa and Teucriuin )iashii (hairs long, 

 simple); Quercus riryiiiiana (stellate hairs on the dorsal surface only): Kiisteletz- 

 kija virginica and Croton maritimus (hairs stehate, scale-like): Phijsidis risco.sa 

 (hairs forked); BorricJtiafrutescens (youngleaves 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 Gramineae). 



Schimper, Pt^anzenge(igr., \). 0".). 



