] ciL^p. Lvii PSAMMOPHILOUS HALOPHYTES 227 



and summer-storms, is colonized by annual herbs, among which many are succulent 

 plants that, apart from this, grow on the salt sea-shore : as examples of these may 

 I be mentioned Cakile americana, Corispermum hyssopifolium, and Euphorbia poly- 

 I gonifolia. Above the high-water mark of winter there commences a sand-field 

 ; composed of species with travelling rhizomes : among such species are Agropyron 

 1 dasystachyum, and Lathyrus maritimus. Added to such species are biennial and 

 I annual herbs, as well as some stunted shrubs. 

 I 

 I Tropical sandy sea-shore has been but httle investigated, but we 



' may note 



Pcs-caprae-association. l^'nder the name ' Pes-caprae formation ', 

 Schimper ^ dealt with that association on the tropical sea-shore in which 

 the convolvulaceous Ipomoea Pes-caprae plays a prominent part. The 

 large-leaved, fleshy, dark-green shoots,- several metres in length, and 

 sometimes decked with large red blossom, creep over the sand, strike root, 

 I and form a frequently close network. In addition, there are several 

 j other species which hkewise for the most part grow over the sand, and 

 do not, like the North-European Carex arenaria, have long creeping 

 rhizomes buried in the sand ; this contrast may be due partly to the 

 circumstance that shifting sand is rarer in the tropics, as the sand is often 

 calcareous (coral) sand composed of heavier and larger grains, and partly 

 to the fact that the wind does not blow so violently as on the northern 

 coasts of Europe. 



CanavaUa-association. In physiognomy the Pes-caprae-association is 

 more or less similar to others, such as the Canavaha-association, which 

 occurs on the Moluccas, according to Warburg, and in the West Indies. 



Among species or genera playing a part on tropical shores may be 

 named the fleshy Sesuvium Portulacastrum ; Altemanthera, Achy- 

 ranthes and Philoxerus vermicularis among Amarantaceae ; Spermacoce 

 and Hydrophylax among Rubiaceae ; Sporobolus virginicus and Cynodon 

 Dactylon among Gramineae ; Remirea maritima and Fimbristylis sericea 

 among Cyperaceae.^ 



On Asiatic shores the blue-green Spinifex squarrosus plays a part 

 similar to that of Ipomoea Pes-caprae, but, like Psamma arenaria in 

 northern Europe, it has a subterranean rhizome ; the large development 

 of its aqueous tissue is probably to be associated with its occurrence on 

 saline soil. The spherical inflorescences, nearly as large as the human 

 head, are extremely light, and possess stiff, elastic, long, spike-axes 

 radiating on all sides ; rolling before the wind and bounding with great 

 leaps over the sand they shed their seeds in the same manner as certain 

 steppe-plants (' wind- witches ').* This plant sometimes forms pure 

 associations to the exclusion of other species. Sometimes a large quan- 

 tity of Nostoc accompanies it. In Ceylon, on the seaward side, it 

 reigns almost alone, but towards the land many other species mingle 

 with it.^ 



Sand on the tropical sea-shore provides examples of creeping perennial 



' Schimper, 1891. 



" Figured in Warming, 1897 ; see also Tansley and Fritsch, 1905. t 



' The anatomy of various species is figured in Warming, 1897. 

 ' Cleghorn, 1858; Gobel, 1889-92. 



' Regarding the morphology of this and other Indian littoral plants, sec Tansley 

 and Fritsch, 1905. 



Q 2 



