724 LECTURE LVni. 



stock, their parts arc extended and evolved from within, and they imbibe their 

 nutriment by superficial absorption only. There is indeed in the crystalliza- 

 _tion of minerals a slight resemblance to a reproduction or generation, wlien a 

 small portion of the substance serves as a basis for the formation of subse- 

 quent crystals: but this portion becomes a constituent part of the crystal, 

 while it preserves its original form; a seed, on the contrary, is a substance 

 naturally and completely detached from the plant, and containing within it- 

 self the simplest rudiments of a new individual, which is afterwards evolved 

 and enlarged. Sometimes, however, vegetables are propagated by means of 

 bulbs, or by spreading roots, by slips, or by ingrafted scions, Avithout a seed de- 

 tached in the regular manner; but in these cases the new plant is much more 

 identical with the old one, than when it is raised from a seed, being as it were a 

 continuation of the same existence. Plants are nourished in great measure by 

 means of their roots; and sometimes, where they are without roots, their nu- 

 triment is probably absorbed by all parts of their surface. 



Animals are distinguished from vegetables by the reception of their food, 

 for digestion and assimilation, into an internal cavity constituting a stomach. 

 The existence of a stomach, calculated for the digestion of food, appears to 

 be the best, if not the only criterion of an animal. Some vegetables, indeed, 

 have a power of catching and detaining animals, by curling up their leaves so 

 as to cover them, as the drosera or sundew, and the dionaea muscipula, or 

 catchfly; but this mechanism can scarcely be intended for their immediate 

 nutriment, at least the leaf can scarcely be supposed to assume the character 

 of a stomach. It is true that we imaaine all animals to have sensation, and 

 all plants to be without it; and if it were possible to discriminate decisively 

 between sensation and irritation, the distinction would supersede every other: 

 but in many cases it is extremely difficult to say where sensation is present, 

 and where irritation only produces the same apparent effects. We cannot be 

 sure that the hydra, or fresh water polypus, or the trichurus sol, an animal- 

 cule described by Dr. Shaw, suffers any sensation of pain when it is diviiled 

 into two parts; at least the pain seems to agree remarkably well with its con- 

 stitution, for it lives and thrives with increased vigour, as two distinct animals. 

 On the other hand, many plants are easily stimulated to perform motions, 

 which have the appearance of muscular actions, influenced by sensation: the 

 sensitive plants close or depress their leaves, in consequence of agitation or of 



