CHAP. LV ADAPTATIONS OF HALOPHYTES 221 



The stomata of true, succulent, littoral halophytic herbs, in cases so 

 far investigated, are not sunken, but usually lie at or near the level of the 

 epidermis. The thickness and cuticularization of the epidermal wall are 

 small in the succulent species : this is worthy of note, and may denote 

 that the atmosphere of the habitat is not very dry, but probably it should 

 be correlated with the fact that protection against transpiration is attained 

 by other means. Exceptions to this rule are provided by tall woody 

 species in mangrove, also by the saxaul-tree (Haloxylon Ammoden- 

 dron), Niederleinia juniperoides, Acantholippia Riojana, 1 and others. 



Storage -tracheids. In addition to what has already been stated 

 regarding the anatomical relations of aqueous tissue, it may be mentioned 

 that, in some species, storage-tracheids apply themselves to the nerve-ends 

 (in several genera belonging to mangrove-swamps), but, in other species 

 (including Salicornia), are isolated in the parenchyma quite apart from 

 the nerves. 2 



Lignification. Except more especially in the case of mangrove- 

 vegetation, lignification occurs only to a sh'ght extent, and in this respect 

 halophytes deviate from other xerophytes. There are, however, several 

 thorny species, in most of which the thorns belong to leaves, as in Salsola 

 Kali, Eryngium maritimum, Echinophora spinosa, Carthamus lanatus, 

 and others ; but these species are possibly confined to sand, which may 

 be responsible for the production of the thorns. 



Idioblasts, in the form of stone-cells, may occur in the palisade or 

 aqueous tissue, for example in Sonneratia, Rhizophora, Carapa, and other 

 mangrove-plants, also in Scaevola Koenigii. 



External Form. According to Lesage's investigation, the height of 

 certain species, Lepidium sativum for instance, decreases on saline soil. 

 Halophytes, as a rule, attain neither great stature nor great circumference. 

 According to the investigations of Stange 3 and others, concentrated 

 salt solutions (not only of common salt, but also of potassic nitrate and 

 glycerine) decrease growth in length, but do not always increase growth 

 in thickness. 



(a) Leaf. Among halophytes there is the same endeavour as in 

 xerophytes to reduce the surface, as is shown by the leaves remaining 

 small. Lesage's experiments prove that an abundance of salt in soil 

 causes leaves to be smaller as well as thicker. The leaves may be linear 

 and semi-terete, as in Suaeda maritima, species of Portulaca, and Salsola 

 Kali ; spathulate and oblong shapes are very common. 4 The leaves are 

 rarely indented, being usually undivided and entire. Some plants, such 

 as Tamarix, are scale-leaved ; others are almost aphyllous stem-succulents, 

 as is illustrated by Halocnemum, Arthrocnemum, and Haloxylon, or, like 

 Ephedra and Casuarina, they remain poor in sap. 



The ericoid 5 form of leaf, with the stomata concealed in a hairy 

 furrow on the lower leaf-face, characterizes the frankeniaceous Niederleinia 

 juniperoides (in the Argentine salt-steppes) and species of Frankenia. 



As in many xerophytes the leaves assume an erect lie, so that when 

 the sun is highest in the heavens its rays strike at acute angles : this, as 

 well as narrowness of the leaves, occasions isolateral leaf-structure : as 



1 Gobel, 1891, p. 13. * Duval-Jouve, 1868 ; Hultberg. 



3 Stange, 1892. * As figured by Warming, 1897. * See p. no. 



