HISTORY OF THE VEGETABLE KINGDOM. 



CHAP. 11. 



THE NATURE AND USKS OF PLANTS. 



Vegetables differ from minerals in being 

 organized bodies, possessed of a degree of life, 

 and capable of taking into their system extran- 

 eous matters, and converting these, by an assim- 

 ilating process into new compounds, which mat- 

 ters are thus rendered subservient to their growth 

 and development. They thus increase their own 

 bulk, and, moreover, throw off from their bodies 

 germs which spring up into other vegetable 

 bodies, the same as the parent plants. Vegeta- 

 bles, also, are under the dominion of the laws 

 of vitality, by which they retain the matters 

 entering into their structure, in a state different 

 from that in which inorganic bodies exist. The 

 matter, too, which enters into the composition 

 of vegetables, is essentially the same as that which 

 forms the structure of animals; the chief ele- 

 mentary ingredients being oxygen, hydrogen, 

 carbon, and azote ; only, the proportions and 

 combinations are somewhat different ; vegetables 

 possessing more carbon and less azote than the 

 generality of animals. In these respects, 

 vegetable bodies closely resemble animals ; in- 

 deed, in the lower divisions of each, the resem- 

 blance is so close, as to render it a somewhat 

 difficult task to point out the distinctive differ- 

 ences. We find no hesitation in drawing a line 

 of distinction between the more perfect plants, 

 and a quadruped, bird, or fish ; but, if we take 

 some animals low in the scale of organization, 

 and compare them with certain simple vegetables, 

 we shall find the resemblance, both of structure 

 and functions, very close indeed. Thus, the 

 Lemna CHbba, or duck weed, a plant which is 

 foimd floating on the surface of the water of 



*.i 



ditches, and slow running streams, has an oval, 

 cellular body a, with several porous roots 5, which, 

 unlike most other vegetables, are unattached to 

 tho soil, but which float in water, and absorb 

 moisture to constitute the juices of the plant. 

 This moisture flows up into the cellular body, 

 and hence, by the medium of pores on the 

 cuticle, or skin, a quantity of air from the atmos- 

 phere is absorbed, and thus converted into the 



proper nourishment of the plant. In the CJ/s- 

 ticercus, c, a species of animal hydatid, which 

 lives within the cavities of the bodies of other 

 animals, there is a neck d, with a tubular 

 mouth, by which the animal draws in the juices 

 on which it feeds, to its stomach. The skin oi 

 this animal is also porous, like the epidermis of 

 the lemna, through which fluids, and perhaps 

 air, are absorbed into its body, to conduce to its 

 nourishment. In the tubipore e, consisting of 

 a branched stem, with numerous cups, each 

 containing a simple animal called a polype, there 

 is a close resemblance to the arborescent form of 

 most vegetables. 



Yet, though plants and animals thus resemble 

 each other very closely, in many essential par- 

 ticulars there are others in which they differ. 

 Thus, in animals which have the power of loco- 

 motion, there is a muscular system, a set of 

 contractile fibres, whose tension or relaxation 

 determines their movements ; in vegetables, there 

 is nothing of the kind. Animals have a stomach, 

 or receptacle, for the substances taken from with- 

 out, in which these are digested before they are 

 carried, by means of the lacteals, into the mass 

 of their circulating fluids ; but in vegetables, 

 nutrition is carried on in a more simple man- 

 ner. The substances absorbed are conveyed 

 directly into all parts of the body, without un- 

 dergoing any previous change, so that, in these, 

 we find neither an intestinal canal, nor a stomach, 

 because there is no proper solution or digestion. 

 In animals there is more or less of a circulation oi 

 the fluids from a centre ; in vegetables the nutri- 

 tious juicesaredifiiised through the plantwithout 

 the agency of a central heart. Plants derive their 

 nourishment from inorganic matters, fr-om air. 

 water, and the various salts of the soil ; animals 

 derive their chief nutriment from matter that has 

 been previously organized, cither fi-om vegetable 

 substances, or the bodies of other animals that have 

 enjoyed an organized existence. Animals have 

 a nervous system and sensation; the meanest 

 animal form shrinks fi'om the touch of an oppos- 

 ing object, and evidently exhibits the indications 

 of pain and pleasure. Plants have no nervous 

 system, neither are they capable of external im- 

 pressions of sensation. Dutrochet, it is true, 

 has pointed out minute granules in plants, which 

 he assumes as analogous to the nervous granules 

 of the lower animals, but this fact has not been 

 yet sufficiently established. As plants perform 

 vital functions so closely allied to the nutritious 

 functions of animals, it is not altogether impro- 

 bable but that some modification, or approach 

 to nervous matter, may be found in their stnic- 

 ture. If this shall be hereafter established, it 

 win not, however, do away with the proposition 

 above, that plants have, in reality, no sensation 

 analogous to that of animals. They have a con- 

 tractile power of their fibres, which acts on the 



