FINAL CAUSED. 13 



volcano, Nature prepares the way for vegetable 

 existence. The sliglitest crevice or inequality is 

 sufficient to arrest the invisible germs that are 

 always floating in the air, and affords the means 

 of sustenance to diminutive races of lichens and 

 mosses. These soon overspread the surface, and are 

 followed in the course of a few years, by successive 

 tribes of plants of gradually increasing size and 

 strength ; till at length the island, or other favoured 

 spot, is converted into a natural and luxuriant gar- 

 den, of which the productions, rising from grasses 

 to shrubs and trees, present all the varieties of the 

 fertile meadow, the tangled thicket, and the widely 

 spreading forest. Even in the desert plains of the 

 torrid zone, the eye of the traveller is often refreshed 

 by the appearance of a hw hardy plants, wdiich 

 find sufficient materials for their growth in these 

 arid regions : and in the realms of perpetual snow 

 which surround the poles, the navigator is occa- 

 sionally startled at the prospect of fields of a scarlet 

 hue, the result of a wide expanse of microscopic 

 vegetation.* 



But whatever charms the naturalist may find in 

 the occupations in which he is engaged, and how- 



* The red snow, discovered in Baffin's Bay on the 17th of August, 

 1818, during the Northern Expedition under the command of Cap- 

 tain, now Sir John Ross, was found to owe its colour to minute 

 fungi, or microscopic mushrooms (Protococcus nivalis), which vege- 

 tate on the surface of snow, as their natural abode. (See Philoso- 

 phical Transactions for 1820, p. 165.) Another microscopic plant, 

 the Pahnella nivalis, is met with on the granular snow, called Firn, 

 of the glaciers of Switzerland. Snow is likewise the natural habita- 

 tion of a minute insect, the Podura nivalis, which is met with in no 

 other place. (Mag, Nat. Hist. iv. 30.) Great numbers of infu- 

 sorial animalcules have also been seen in melted snow. (Silliman's 

 Journal, xviii. 56.) 



