564 THE UNIVERSE. 



bare. Its most elementary representative forms first ap- 

 pear on the naked rock; the air seems almost to suffice 

 for their nourishment: these are the lichens and the micro- 

 scopic fungi. Then appear mosses, which, leaving mould 

 behind them as they decompose, form for the future a soil 

 thick enough to nourish the grasses. Lastly come shrubs 

 and bushes, and then a verdant forest is soon seen rising 

 in a district formerly stricken with sterility.^ 



The vital resistance of seeds, which varies between the 

 widest extremes, comes also to the aid of dissemination. 

 In fact, while there are some grains the organic develop- 

 ment of which seems as if it could not be checked, and 

 which are so impelled towards Ufe that they germinate 

 even on the plant which produces them, as we have seen 

 is the case with the Ehizophorre; there are others which 

 on the contrary yield embiyos in the bosom of which life 

 may slumber through a succession of ages. 



The seed of the coffee-tree, notwithstanding the thick 

 coriaceous covering of its embryo, in a very short time 

 loses the power of germinating. Should the planter defer 

 sowing only for a few days, the seed will be incapable of 

 reproduction. 



But on the other hand some seeds, apparently less 



1 In my youth I travelled through the celebrated valley of Golduu in Switzer- 

 land, where, twenty j'ears previously, a whole mountain had given way in the 

 most frightful manner, crushing several villages, and covering an immense space 

 with fragments of broken rocks. All these rocks, lately quite bare, were alreadv 

 covex-ed with a luxuriant vegetation, and the tortuous and uneven road whicli 

 had been cleared through this vast sheet of ruin, was everywhere smiling and 

 fresh, and covered with pines and shrubs of the most charming aspect. M. 

 Boussingault mentions a similar instance which he observed in America. In ten 

 years a mass of porphyry rocks, which had fallen down, was covered with massive 

 acacias. — Boussingault, Economie Rurale. [Lees, on weighing together and sepa- 

 rately a tuft of Bryiim capillare and the soil attached to it, found that it had 

 collected and retained on the tiled roof where it grew five times its own weight 

 of humus. — Te.1 



