72^ LECTURE LVIII. 



The vegetable kingdom presents to us a spectacle highly interesting by its 

 variety and by its elegance; but the economy of vegetation appears to be lit- 

 tle diversified, although little understood. With respect to the apparent per- 

 fection of their functions, and the complication of their structure, we may 

 consider all vegetables as belonging to two principal divisions, in one of 

 ■which the seed is prepared with the assistance of a flower, having its stamina 

 and its pistils, with petals or a calyx; while in the other, the preparation 

 of the seed is less regular and conspicuous, and hence such plants are called 

 cryptogamous. In some of these there is a slight resemblance to the flowers of 

 other vegetables, but on the whole, the class appears to form one of the con- 

 necting links between the three kingdoms of nature; its physiology is proba- 

 bly simple, but it has been little examined. The herbs, palms, shrubs, and 

 trees, which constitute the numerous genera of flowering vegetables, exhibit 

 the greatest diversity in the forms and dispositions of the organs of fructifica- 

 tion, while they have all a general resemblance in their internal economy. 



Every vegetable may be considered as a congeries of vessels, in which, by 

 some unknown means, the aqueous fluids, imbibed by its roots, are subjected 

 to peculiar chemical and vital actions, and exposed in the leaves to the in- 

 fluence of the light and air; so as to be rendered fit for becoming constituent 

 parts of the plant, or of the peculiar substances contained within it. 



The first process in the germination of a seed is its imbibing moisture, and 

 undergoing a chemical fermentation, in which oxygen is ab*orbed, and a part 

 of the mucilage contained in the seed is converted into sugar; a substance 

 probably more nutritive to the young plant. The radicle shoots downwards, 

 and the seed leaves, or cotyledons, which are generally two, although some- 

 times more or less numerous, raise themselves above the ground, till in a 

 short time they die and drop off, being succeeded by the regular and more 

 adult leaves. 



In every transverse section of a vegetable, we commonly discover at least 



four different substances. The parts next to the, axis of the tree or branch 



consist of medulla or pith, which is supposed by some to be the residence of 



the vegetable life of the plant; but a tree may live for many years after be- 



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