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 familiar, because it is bor- 
rowed from his own science. On the other hand, the botanical stu- 
dent, in learning 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 
sohd 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 sensibility hke 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 fife 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 shall now treat of the solid portions of the vegetable organi- 
zation; these are all 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— Its language borrowed from animal physiology— Different 
aspects of vegetables to the careless observer and the philosopher — Diflacult to deter 
mine where vegetable life commences— Solid parts of plants. 
