222 



HALOPHYTES SECT, vn 



examples may be cited Atriplex (Obione) portulacoides, Suaeda mari- 

 tima, Sesuvium Portulacastrum, and some species in mangrove. 1 In the 

 verbenaceous Lippia (Acantholippia) Riojana the leaves are appressed ; 

 and between the leaf and stem hairs occur, while on the assimilatory 

 outer side of the leaf there are deep, hairy furrows. 



(&) Stems. The stems of halophytes are often prostrate, radiating 

 on all sides from a common point, which is the base of the main axis. 

 This may be observed in species of Atriplex, Suaeda, Salsola, and other 

 Chenopodiaceae, in Polygonum Persicaria and its allies, Senecio vulgaris, 

 and other plants on European shores. This is not caused by wind, since 

 the stems take no definite constant direction ; the great irregularity 

 prevailing points to local influence, which is certainly to be attributed to 

 the differential heating of the frequently stony soil. 2 



The majority of the structural peculiarities just mentioned also occur 

 in xerophytes. There thus exists a remarkable agreement between 

 halophytes and xerophytes, as Schimper was the first to point out ; both 

 these types of plants dry slowly when exposed to strong evaporation and 

 aridity ; such is the experience of every one who has tried to dry succulent 

 species for the herbarium. But this slowness of drying is due not only 

 to the devices guarding against rapid transpiration, but also, in the 

 case of halophytes, to the saline cell-sap which evaporates more slowly 

 than pure water. Moreover, in matters floristic, certain features in 

 common have been demonstrated for instance, the occurrence of the 

 same species on the sea-shore and on mountains. 



What is the reason for this remarkable agreement between xerophytes 

 on non-saline soil and halophytes which may even grow on soil saturated 

 with water, as is the case with Salicornia-vegetation on the coasts of the 

 North Sea at high tide, and with mangrove-plants at all times ? Schimper 3 

 directs attention to the deleterious action of common salt in the cell-sap 

 upon assimilation and upon the life of the plant as a whole ; and this 

 has been experimentally proved. 4 Common salt behaves as a poison to 

 the plant, because it is readily absorbed in large quantities and then acts 

 lethally. In order to prevent an excess of chlorides from being conveyed 

 to the leaves by the transpiration-current and deposited in the cells, the 

 plant must, according to Schimper's explanation, guard against intense 

 transpiration, and therefore requires the many protective devices already 

 described. It is doubtful if this explanation be correct ; for, supposing 

 that transpiration were extremely slow and weak, but nevertheless 

 prolonged, quantities of salt would certainly accumulate in the plant 

 until finally an injurious amount was present ; it might then be that 

 the plant would possess means by which to decompose and dissipate 

 the absorbed salts and such is apparently the case according to Diels. 5 

 If Diels be correct (which Benecke 6 denies) the xerophytic structure is 

 probably designed to obstruct the free gaseous interchange between the 

 tissue and atmosphere, so that, as in the case of succulent plants, there 

 may be formed in the tissue malic and other organic acids, which in this 

 instance would serve to decompose the chlorides. 



1 According to Johow (1884), Karsten (1891), Warming (18976), and Schmidt 

 (1899, 1903). * See p. 27. 



3 Schimper, 1890, 1891, 1898. * Kearney, 1902. 



* Diels, 1898. 6 Benecke, 1901. 



