18 Vegetable Physiology. 



the whole plant, the flowers which produce seed necessary for 

 its reproduction, are termed organs, while the effects produced 

 by these parts are called their functions. All bodies which 

 possess these or analogous parts, are called organic, while 

 those which do not, are inorganic. Some of the functions of 

 organic bodies are subject to the same laws which operate on 

 inorganic matter. For instance, the principle on which the 

 blood is propelled by the heart through the arteries is the same 

 on which water may be driven through a series of pipes by a 

 pump. But the nature of the force is entirely different In 

 the latter case, it is merely mechanical. In the former, it is 

 produced by a property peculiar to organized structure, and 

 especially belonging to muscle — that of contracting when it 

 receives a certain stimulus or irritation. This property, and 

 many others which are never displayed by inorganic bodies, 

 are called vital, and it is by means of these that those changes 

 are effected which constitute the life of an animal or plant. 

 These properties of organized bodies operate only under cer- 

 tain conditions. A seed may remain for centuries in a dor- 

 mant state, and may never become any thing but a seed. As 

 soon, however, as it is laid where it can receive moisture, 

 warmth, and air, it will begin to germinate. These, then, are 

 the conditions required to produce in it vital action, or those 

 changes which are termed Life. In case the plant, after it has 

 begun to grow, under these influences, be placed entirely out 

 of their reach, it either dies, or remains inactive for a time, 

 until returned to its former position. Light, warmth, and 

 moisture, for these reasons, are called the stimuli to vital 

 action. In our considerations, therefore, are naturally com- 

 prised that of the structure of plants, of the properties which 

 belong to that structure, and of the operation of external stimuli 

 upon those properties. 



It will be perceived here, that the distinctions so far ex- 

 plained, between organic and inorganic bodies, apply as well 

 to animals as to plants. Before proceeding to our main sub- 

 ject, then, it will be proper as well as interesting to trace some 

 of the less general distinctions by which is produced the dif- 

 ference between these two grand divisions of organized mat- 

 ter. It is sometimes by no means easy to point out such a dif- 



