66 Estahlishment of Vegetation at the Surface of the Globe. 



diacece, fungi, &c. They constitute a great and important fa- 

 mily in the natural order of vegetation. Linnaeus has named 

 them cryptogamous plants, from the circumstance that the mode 

 of fecundation, by which they are reproduced, is very little 

 known. 



The byssi are plants which present themselves only under the 

 form of a powdery tissue, or of a filamentous down, variously 

 coloured ; they attach themselves chiefly to moist substances, dry 

 up in the rays of an ardent sun, and leave behind them only 

 formless and blackish spots. The conftrv(E belong to stagnant 

 waters and inundated lands ; they are composed of capillary elon- 

 gated filaments, simple or articulated. The lichens are some- 

 times nothing else than prominent blackish points, scattered up- 

 on a greenish or greyish ground ; at other times they are simple 

 or branched lines, which have the semblance either of alphabe- 

 tical characters, or of a sort of geographical chart, marked upon 

 a very thin smooth membrane, applied to the bark of trees. 

 Other species attach themselves to rocks, forming plats of va- 

 rious colours, leprous, granular, or powdery crusts ; or assum- 

 ing a greater degree of development, spread out into rosaceous 

 expansions of a foliaceous aspect, with laciniated or lobated 

 margins. Some of them rise from a scaly crust, in the form of 

 simple stems, or ramify into small elegant shriibs, dilated at their 

 summits into little cups, which are either simple or proliferous, 

 and which are furnished upon their edges with fungous tuber- 

 cles, of a brown or blackish colour, or of a beautiful scarlet red. 

 Others present themselves under a very diff^erent form, falling 

 from the trees in long intermingled filaments, like horse's hair or 

 tufted locks ; some of a greyish green, others of a beautiful gold 

 yellow, orange or lemon. I shall not extend my remarks upon 

 this class of plants, with which we shall have to form an acquaint- 

 ance in another place, when we come to treat of the natural fa- 

 milies. Here we shall speak of them only with relation to the 

 great functions which nature has confided to them for the esta- 

 blishment of vegetation. 



When we remark the hardness, the dryness, and the bareness 

 of rocks, we should scarcely imagine that their summit might 

 one day be crowned with forests ; and yet this great work is car- 

 ried on every day under our eyes, and even in the midst of our 



