40 THE PHILOSOPHY 



retarded ; and their fickly colour indicates a defecft of vigour. 

 Plants, when placed in fimilar circum fiances, are always weak, 

 dwarfifh, and unnaturally coloured. But exercife is equally 

 necelTary to the health and vigour of plants, as it is to thofe 

 of animals. The exercife of animals is effecled by various 

 kinds of fpontanecus motion. Plants are likcwife exercifed 

 by motion ; but that motion is not voluntary ; it is commu- 

 nicated to them by the a6lion of the air. The agitation 

 which they receive from the winds enables them to extend 

 their roots, prevents them from a growth too rapid, and, of 

 courfe, ftrengthens their whole fabric. It is owing to the 

 want of this agitation, that plants brougiit up in houfes, or 

 in other conhned fituations, flioot out to an unnatural length ; 

 that their ftems and branches are always flender and weak ; 

 and that they ripen not their fruit like thofe which are expo- 

 fed to the open air. 



To conclude this branch of the fubjeiSt, plants and animals 

 are fo nearly allied^ that their grov/th and nourifhment are 

 not only effecled by fimilar inflruments, but fome parts of an- 

 imal bodies evidently partake of a vegetable nature. Thus, 

 the hairs, the nails, the beaks, and the horns, are a fpecies of 

 vegetables, as appears from their comparative total infenfibil- 

 ity, as well as from the mode of their growth and repro- 

 duction. 



III. DISSEMINATION and DECAY. 



WE fhall next take an analogical view of the difTemination 

 and decay of the animal and vegetable. 



The power of reprodu(^ion is peculiar to the plant and 

 animal. Each of them is capable of producing beings every 

 way fimilar to the parent. But the modes by which this fln- 

 gular effect is accompliflied, are very different in appearance. 

 It is our prefent purpofe to remove this apparent difference, 

 and to fhow that animals and vegetables multiply their fpecies 

 in a manner extremely analogous. 



