46 THE VITAL FUNCTIONS. 



giving rise to the appearance of a ring bare of grass, sur- 

 rounding the dark ring; but after the fungi have ceased to 

 appear, the soil where they had grown becomes darker, and 

 the grass soon vegetates again with peculiar vigour. When 

 two adjacent circles meet and interfere with each other's 

 progress, they not only do not cross each other, but both 

 circles are invariably obliterated between the points of con- 

 tact: for the exhaustion occasioned by each obstructs the pro- 

 gress of the other, and both are starved. It would appear 

 that different species of fungi often require the same kind of 

 nutriment; for, in cases of the interference of a circle of 

 mushrooms with another of puff-balls, still the circles do not 

 intersect one another, the exhaustion produced by the one 

 being equally detrimental to the growth of the other, as if 

 it had been occasioned by the previous vegetation of its 

 own species. 



The only final cause we can assign for the series of phe- 

 nomena constituting the nutritive functions of vegetables is 

 the formation of certain organic products calculated to sup- 

 ply sustenance to a higher order of beings. The animal 

 kingdom is altogether dependent for its support, and even 

 existence, on the vegetable world. Plants appear formed 

 to bring together a certain number of elements derived from 

 the mineral kingdom, in order to subject them to the ope- 

 rations of vital chemistry, a power too subtle for human 

 science to detect, or for human art to imitate, and by which 

 these materials are combined into a variety of nutritive sub- 

 stances. Of these 'substances, so prepared, one portion is 

 consumed by the plants themselves in maintaining their 

 own structures, and in developing the embryos of those 

 which are to replace them; another portion serves directly 

 as food to various races of animals; and the remainder is 

 either employed in fertilizing the soil, and preparing it for 

 subsequent and more extended vegetation, or else, buried in 

 the bosom of the earth, it forms part of that vast magazine 

 of combustible matter, destined to benefit future communi- 

 ties of mankind, when the arts of civilization shall have de- 

 veloped the mighty energies of human power. 



