LECTURE XVII. 



Physiological Views. 



HAVING considered the organs of the plant, from the root to 

 the seed, it might seem as if our inquiries into the vegetable 

 substance were terminated ; but we have yet to investigate 

 more minutely the internal texture of these various organs. 

 Before commencing the study of botany, when you looked at 

 the trunk of a tree, a little herb, or a leaf, you perhaps con- 

 sidered it as very simple in its structure ; you saw it only as 

 one mass : but you now perceive that plants, like animals, are 

 collections of fibres ; that they have parts which are analogous 

 to our skin, bones, flesh, and blood ; that they are living, or- 

 ganized beings, composed of solid and fluid parts ; and are, like 

 animals, the subjects of life and death. 



Plants differ from animals in not possessing any of the or- 

 gans of sense. They can neither see, hear, taste, smell, nor 

 touch. Some vegetables, however, seem to have a kind of 

 sensibility like that derived from the organs of touch ; they 

 tremble and shrink back upon coming in contact with other 

 substances ; some turn themselves round to the sun, as if en- 

 joying its rays. There is a mystery in these circumstances 

 which we cannot penetrate, and it is not yet fully known at 

 what point in the scale of existence animal life ends, and vege- 

 table life commences. Some animals, like the sponge and 

 corals, seem almost destitute of any kind of sensation, and yet 

 they are ranked in the animal kingdom. On the subject of the 

 distinctions and analogies between plants and animals, we shall 

 dwell more fully hereafter. 



Solid parts of Vegetables. 



At present we have to consider the solid parts of the vegeta- 

 ble system ; these are all composed of a membranous substance, 

 which exists in every part of the plant, forming by various mo- 

 difications, the different textures which the vegetable system 

 exhibits. This membranous substance appears chiefly under 

 two elementary forms : viz. 1st, that of tellular texture ; 2d, 

 vascular texture. 



Object of the 17th lecture Plants analogous to animals Difficult to deter- 

 mine where vegetable life commences Solid parts of plants Membranous 

 substance under two forms. 



