SOLID PARTS OF VEGETABLES. 107 



The subjects upon which, in this lecture, we have been engaged, 

 properly come under the head of vegetable physiology, a depart- 

 ment of botany highly interesting, but too complicated in its nature 

 to be, to any great extent, presented to the mind of the youthful in- 

 vestigator. The physician finds in the vegetable organization strik- 

 ing analogies to the internal structure of the animal frame ; to him 

 the language of physiological botany is famiUar, because it is bor- 

 rowed froin his own science. On the other hand, the botanical stu- 

 dent, in leai-ning the names and offices of the various internal 

 organs of plants, is making no inconsiderable improvement in the 

 knowledge of the animal economy, and stupid must be that mind 

 which is not, by the consideration of the one, led to reflect upon the 

 organization of the other. 



LECTURE XVIII. 



PHYSIOLOGICAL VIEWS — SOLID AND FLUID PARTS OF VEGETABLES. 



The careless observer of nature may consider the trunk of a tree, 

 a leaf, or a stem of an herb, as very simple in its structure, present- 

 ing little more than a homogeneous mass ; but the botanical philos- 

 opher looks with a far different eye upon the vegetable being. He 

 has learned that plants, like animals, are formed of vessels of dif- 

 ferent kinds, variously fitted to carry on the operations of imbibing 

 nourishment, of making a chemical analysis of the same, and of 

 appropriating to themselves such elements as are necessary to pro- 

 mote their health and vigour, and of rejecting such as are useless. 

 In short, that they have parts which are analogous to skin, bones, 

 flesh, and blood: that they are living, organized beings, composed of 

 solid and fluid parts; and, like animals, the subjects of life and 

 death. 



Plants differ from animals in being destitute of the organs of 

 sense. They can neither see, hear, taste, smell, nor touch. Some 

 vegetables, however, seem to have a kind of sensibihty like that de- 

 rived 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 enjoying its rays. There is a mystery in 

 these circumstances which we cannot penetrate; it is not yet fully 

 known at what point in the scale of existence animal life ends, and 

 vegetable life commences. Some beings, like the sponge and corals, 

 seem almost destitute of any kind of sensation, and yet they are 

 ranked among animal substances. The subject of the distinctions 

 and analogies between plants and animals, we shall consider more 

 extensively hereafter. 



Solid parts of Vegetables. 

 "We shafl now treat of the solid portions of the vegetable organi- 

 zation ; these are afl composed of a membranous substance, which 

 exists in every part of the plant, forming by its various modifica- 

 tions, the different textures which the plant exhibits. This mem- 

 Vegetable Physiology— lis language borrowed from animal physiology— Different 

 aspects of vegetables to the careless observer and the philosopher— DiflBcult to deter 

 mine where vegetable life commences — Solid parts of plants. 



