180 The Influence of the Soil 



Many of the saxifrages which are found upon the calcare- 

 ous soil, present exudations of carbonate of lime, analogous 

 to those of the Chara. These exudations appear under three 

 different forms. Upon the Saxifraga Aizoon, and upon the 

 analogous species, we find, all along the edge of the leaves, 

 little cavities filled with carbonate of lime ; upon S. cassia are 

 small holes placed on the upper surface of the leaf, in which 

 the salt is deposited in successive layers, from the bottom to 

 the top ; the under surface is pierced with numerous stomata, 

 which, from their number, seem designed to supply the im- 

 perfect evaporation of the upper surface. 



The plants peculiar to the argillaceous schist, are less nu- 

 merous than those of the calcareous strata ; this may be attri- 

 buted to the slight affinity of plants for alumina, which is 

 never found in them except in infinitely minute quantities. — 

 We may admit the following : — 



Blechnum boreale Veronica bellidioides 



Sesleria disticha Rhododendron ferrugineum 



Juncus trifidus Sibbaldia procumbens 



Hieracium grandijlorum Phaca astragalina 



H. intybaceum P. australis 

 Phyteuma hemispharicum 



Upon the grauwacke and red sandstone we notice plants 

 from both the calcareous and argillaceous beds ; their number 

 depending upon the manner in which the former formations 

 may have been modified by being in contact with the latter. 

 If upon the granite or gneiss, we sometimes by chance meet 

 with plants belonging to the calcareous strata, a careful exa- 

 mination of the rock will explain their occurrence ; it was in 

 this manner that, having observed the Sesleria ccerulea upon 

 the hornblende, and Gpysophila repens upon granite, I ascer- 

 tained that these rocks were in a state of decomposition, ow- 

 ing to the presence of acids. I ought, however, to confess, 

 that I have sometimes found the Dryas octopetala, Saxifraga 

 oppositifolia, Hieracium villosum, and the beech, upon the 

 same strata, without being at all able to account for their de- 

 velopement, except in calling to mind that Hugi, Wahlenberg, 

 and myself, have observed plutonic rocks covered with a light 

 calcareous bed, which time had caused to disappear after the 

 dev elopement of the plant. If it be incontestible that the na- 

 ture of the soil influences the principles which are found in 

 vegetables, we have reason to suspect that it may also have 

 an influence upon the forms of plants. I here give lists of 

 some varieties, which I consider the simple consequences of 

 the different nature of the subjacent strata. 



