241 



death here ; their decay prepares the soil for the elegant little alpine 

 moss, the destruction of which is speedily followed by the appearance 

 of greener and more luxuriant mosses, until sufficient soil has been 

 formed for the whortle-berry, the juniper, and finally for the pine. 

 Thus, from an insignificant beginning, an ever-increasing coating of 

 humus grows up over the naked rock, and a vegetation, continually 

 stronger and more luxuriant, takes up its position, not to be nourished 

 on that humus, which increases instead of decreasing with every de- 

 caying generation, but by its means to be supplied with nourishment 

 from the atmosphere." — p. 162. 



But that this fertilizing humus is of itself incapable of furnishing 

 the requisite pabulum to all plants indifferently, is evident from the 

 scanty vegetation of localities where it abounds; and that it is not of 

 itself the only requisite for a luxuriant vegetation is also evident from 

 the number of plants which flourish where the soil contains but a 

 small proportion of humus. 



" When we look to the wild vegetation of our own latitudes, we 

 find two principal classes of soil : one a peat or bog soil, which con- 

 sists almost wholly of humus, therefore of decomposed organic mat- 

 ter, the other of calcareous, sandy, or argillaceous soils, in which the 

 inorganic constituents prevail in so great a degree, that the humus, in 

 the blackest soils, does not amount to more than 10 $■ cent, at most, 

 and even in the most fertile, and those clothed with the richest vege- 

 tation, often scarcely forms J $• cent. And that peat or bog soil, so 

 rich in humus, can only afford sustenance to 300 of the 5,000 flower- 

 ing plants growing in central Europe ; and there are not perhaps 

 fifty plants, therefore not one per cent., of which the actual conditions 

 of healthy growth are furnished by the bog soil, which would not also 

 thrive exceedingly well in other places, if the necessary moisture 

 were afforded them. * * On the other hand, the other class 



nourishes the whole vegetation of our latitudes, in a multiplicity 

 which is varied enough to our eyes, unused to the tropical world, and 

 we generally find the richest abundance on the soils which are poor- 

 est in humus, but richest in inorganic constituents, on basaltic, grani- 

 tic, porphyritic and calcareous soils." — p. 167. 



As a general summary we may quote one more paragraph from this 

 lecture, of which we fear our readers are by this time heartily tired. 



" We have, then, three opposite conditions here : the common soil, 

 bog soil, and that of gardens. The first nourishes an abundance of 

 different plants, which, however, remain the same, in fixed conse- 

 quence, through thousands of years. The bog soil is extraordinarily 



