MARINE PLANTS. 15 



those on its northern side ; a chalk district pre- 

 sents an array of vegetation greatly differing from 

 that of a clayey soil ; which, again, as widely 

 differs from pastures in the immediate neigh- 

 bourhood of the sea. Vines cannot flourish in 

 a soil which does not supply them with potash ; 

 neither can peas, beans, nor plants used as dyes, 

 reach perfection without the same ingredient. 

 The corn plants require a soil containing both 

 potash and the earthy phosphates ; nor can any 

 of the grasses flourish without silica, which 

 gives its hard coating to straw, and to so 

 great an extent is it absorbed by them, that 

 hard masses of vitrified silicious matter have 

 been found where a wheat or hay-stack has 

 been destroyed by fire ; and the hollow tubes of 

 the bamboo often contain solid flinty lumps, 

 called in India " Tabaslieer." Plants of the 

 cruciform order (as mustard, turnips, etc.) con- 

 tain sulphur, and require it in a soil in which 

 they can flourish. In fact, most plants have 

 their peculiarities in this respect, and often 

 there is a marked difference in the trees grow- 

 ing on the same mountain, depending on the 

 nature of the rock beneath. 



Let us now take a glance at the various 

 habitats, (as they are termed by botanists,) and 

 the chief plants which occupy them. 



Marine plants are those which are found in 

 sea-water, and therefore in every ocean. It is 

 not to be supposed that plants grow indif- 

 ferently at any depth in the sea ; it is probable 

 that they will not exist at a greater depth than 



