MARINE BOTANY. Ill 



CHAPTER III. 



While terra Jirma develops its richest plans on the lowest 

 spots — in plains and in bottoms — and the size and variety 

 of its growth decreases in the loftier mountainous regions, 

 till at last all vegetation dies out, we find quite a different 

 arrangement in the Ocean empire. Here the greatest depths 

 are plantless, and the calcareous nullipores, mosses, and 

 lichens, are not found below a depth of from six to eight 

 hundred feet. Gradually, corallines and other varieties of 

 sea- weed join them, till the rich girdle of plants which the 

 sea displays on its frontiers commences about one hundred 

 feet below the surface of the water. The plants which form 

 it stand, it is true, at a lower stage of development than 

 those of the land, and lack the splendour of the flowers and 

 fruits ; but, just as the earth ever appears in a new garb at 

 different heights and latitudes, and attracts our highest 

 admiration by the unending multiplicity of its ornaments, 

 so the forms of the Algse change, both in descending from 

 the highest bed to the depths, and in moving along the 

 coast ; and the leaves of these marine plants are deficient 

 neither in beauty of colour, nor in gracefulness of form. 



The different media in which land and marine plants live 

 necessarily demand equally different modes of support. The 

 former principally employ their roots to draw nourishing 

 essences from the lap of earth : the Alga?, on the other hand, 

 imbibe along their entire surface the materials needed for 

 their support, and the roots are only employed for adhesion. 

 The peculiar constituents of the soil are very important to 

 the land plant, for it lives partly on them ; with the marine 

 plant, it is a matter of indifference whether the ground on 

 which it grows is composed of granite, chalk, slate, or sand- 

 stone, if it only afford safe anchorage. 



Flat rocks, which are not too greatly exposed to the pres- 



