THE NATURE AND USES OP PLANTS. 



application of external stimulants, remarkably 

 displayed, in tlie sensitive plant, and in the 

 turning of leaves and tendrils towards the light 

 and air ; this, which has been termed irritability, 

 is widely different from the true sensitive percep- 

 tions of animals. 



But, though vegetables thus differ materially 

 from animals, in having no sensation, nor any 

 medium of communication with external things, 

 they yet are possessed of the essential properties 

 of life. Like animals, they are acted upon by 

 the external agencies or stimuli of life, as heat, 

 light, air, moisture, and electricity ; and the vital 

 laws by which they are governed, place them in 

 a totally different position from inorganic matter. 

 In the tubes of vegetables, the sap ascends from 

 the earth, contrary to the laws of gravity ; and 

 the juices, and the whole material of the plant, 

 as long as it is possessed of life, resist the com- 

 mon chemical laws of decomposition : but, when- 

 ever it is cut down, or deprived of life, these 

 juices immediately run into fermentation, and 

 again return to the elementary matters of which 

 they were originally composed. Vegetables are 

 destitute of voluntary motion. Some of them, 

 however, execute a species of locomotion, or 

 very simple change of place. The Lemna, or 

 duck weed, floats in water, yet this is merely a 

 passive motion. The roots of many of the family 

 of the Orchis, have two fleshy tubercles placed 

 side by side, at the base of the stem. One of 

 these tubercles, after giving birth to the stem, 

 whose germ it contained within it, withers, con- 

 tracts, and ultimately perishes. But, in propor- 

 tion as it disappears, a third grows out close to 

 that part which still contains the rudiments of 

 the stem, which is to appear in the following 

 year, and replaces the former when it has van- 

 ished. In this development of a new tubercle 

 occurring each year, on one side of those which 

 already exist, it wiU be seen that, when a new 

 stem is produced, it is removed by a certain 

 space from that which preceded it. The same 

 thing happens, and nearly in the same manner, 

 in regard to the meadow saffron, with the ex- 

 ception that its bulbs tend continually to sink 

 deeper and deeper in the earth. 



The number of vegetable forms on the surface 

 of the globe is immense. At least 60,000 dis- 

 tinct species have already become familiar to 

 botanists, and as every new exploration of re- 

 cently discovered regions is adding rapidly to 

 the list, the probability is, that at least twice 

 this number exists in nature. The past history 

 of the earth, too, informs us that many vege- 

 table forms, which once flourished in great lux- 

 uriance and profusion, are now swept from the 

 soil, and no longer exist, but in their fossil forms 

 in the rocks and strata. 



As is the case in the animal kingdom, we 

 find that the tribes and families of vegetables 



vary exceedingly in their forms and sizes. Some 

 are so minute as to be invisible to the naked 

 eye, others rise to the height of 150 and 200 

 feet, and occupy an area of several square yards 

 with their ramifying foliage. 



The lowest tribes of vegetables are not only 

 minute, but very simple in their structure. The 



blue mould a, found in bread and other farinaceous 

 articles of diet, when examined by the microscope, 

 will be seen to consist of a number of upright 

 stalks, surmounted by a spherical ball at the 

 top. This mould is in fact a species of fungi, 

 and the round heads contain innumerable small 

 black seeds or sporules, which, when the plant 

 has arrived at maturity, burst from their cover- 

 ing, are scattered about, and floating through 

 the atmosphere, are ready to fall upon other 

 pieces of bread, and grow up into fresh fungi. 

 If an apple is cut across, and allowed to remain 

 in a damp situation for a few days, the surface 

 win also be covered with a mould of a similar 

 character. The fungi here have even more of the 

 arborescent form, and approach somewhat to the 

 mosses. Figure h represents the apple mould ; 

 c, the pear mould. The gray lichens which so abun- 

 dantly encrust rocks and stones are also simple 

 vegetables, produced from a small seed, which, fix- 

 ing itself on the flinty rock, by means of a tough 

 mucilaginous juice, becomes the centre from 

 whence others radiate, till a large circular patch is 

 produced. Mosses and ferns are vegetables some- 

 what more complicated ; and hence we ascend 

 to herbs and shrubs, the towering palm and 

 the majestic oak of the forest. 



The use of vegetable products to man, and 

 other higher animals, is obvious to every one. 

 The paramount importance of the vegetable king- 

 dom, as forming an essential link in the great 

 system of nature, may be very shortly pointed 

 out. 



Vegetables clothe the surface of the soil, af- 

 fording protection to the smaller animals, mi- 

 tigating the arid effects of the sun, and prevent- 

 ing the disintegration of surface fi-om the effects 

 of the elements. They also preserve the purity 

 of the atmosphere, absorbing the excess of car- 

 bonic acid, generated by the respirations of ani- 

 mals, and giving out, by the decomposition of 

 water, a quantity of oxygen to make up for 

 that consumed by the animal kingdom. Vege- 



