GENERAL INTRODUCTORY REMARKS 219 



(perhaps one per cent.) of salt may expel all plants save halophytes, 

 whereas if the soil does not dry readily 2-3 per cent, of salt is required 

 to act in the same manner. 



The following families are halophilous : Chenopodiaceae, Aizoaceae, 

 Plumbaginaceae, Portulacaceae, Tamaricaceae, Frankeniaceae, Rhizo- 

 phoraceae, and Zygophyllaceae. In addition the following are often 

 represented on saline soil : Cruciferae, Caryophyllaceae, Euphorbiaceae, 

 Cyperaceae, Gramineae, Malvaceae, Primulaceae, Asparageae, Compositae, 

 and many others. Some genera are nearly world-wide in distribution, 

 though represented by different species. 



Markedly halophobous are : Betulaceae, Fagaceae, Piperaceae. 

 Urticaceae, Rosaceae, Ericaceae, and Araceae. Furthermore, mosses 

 and lichens do not thrive well upon saline soil. 



CHAPTER LV. ADAPTATIONS OF HALOPHYTES 



Duration of life. Into the composition of halophytic vegetation 

 there enter annual and perennial herbs, as well as woody species, including 

 shrubs and trees. The number of annual species seems to be large ; 

 for instance, in the north of France, according to Masclef , x of the thirty-five 

 species confined to saline soil twenty are polycarpic suffruticose herbs, 

 the remainder, or nearly half, being monocarpic ; the like is true of 

 Denmark ; and in the Spanish peninsula, according to Willkomm, about 

 one-third of the halophytes are annuals. The reason for this prepon- 

 derance is unknown ; probably it is indirectly due to the circumstance 

 that halophytic vegetation is usually very open and thus provides space 

 for such annual species. 2 



Anatomy. Attention has already been directed on p. 134 to the 

 very close agreement in external and internal structure between halophytes 

 and xerophytes : this agreement exists because salt in the soil renders 

 it physiologically dry ; a halophyte, in fact, is one form of xerophyte. 



Some of the morphological and anatomical characters that are shown 

 by xerophytes and reappear among halophytes 3 are 



Succulence. The most striking feature among halophytes is that they 

 are nearly all succulent plants : the leaves are thick, fleshy, and more or 

 less translucent. This is due partly to the abundance of cell-sap and 

 Poverty in chlorophyll, but partly to smallness of the intercellular spaces. 

 It has long been known that certain species are dimorphous, showing the 

 maritime or halophytic form with juicy, thick leaves, and the ordinary 

 inland form with thin leaves : among such species are Lotus corniculatus, 

 Geranium Robertianum, Convolvulus arvensis, Matricaria inodora, 

 Hieracium umbellatum, Solanum Dulcamara. Culture-experiments 4 

 have shown that certain halophytes grown on ordinary soil poor in salt 

 acquire thinner leaves and lose other characteristics such is the case 

 with Cakile maritima, Cochlearia ofncinalis, Salicornia herbacea, Spergu- 



1 Masclef, 1888. 



3 The production of seed is a most effective method of protection in such halo- 

 phytic areas. * Warming, 1897, 1906 ; Schimper, 1891 ; Kearney, 1900. 



4 Batalin, 1884; Lesage, 1890; Boodle, 1904. 



