xlvi INTRODUCTION TO BOTANY, 



tached from the parent plant, become developed, and produce 

 a vegetable exactly similar to that from which they derive 

 their origin. Plants of this kind bear the name of viviparous. 

 In bulbils there is no embryo. 



The uses of buds, bulbs, &c. are various ; for example, in 

 domestic economy, the genus allium, including the onion, 

 garlick, &c. ; in medicine the squill-bulb, is a powerful expec- 

 torant, and diuretic. 



Of Leaves, 



The arrangement of leaves in the bud is called prefoliation. 

 Genera are sometimes well arranged from this into natural 

 families. Leaves, as considered after their developement, by 

 the numerous pores on their surfaces, serve for the purpose of 

 exhaling and absorbing the gases, (airs,) which are either 

 become useless, or which are adapted for the nutrition of the 

 vegetable. Leaves seem to be formed by the expansion of a 

 bundle of fibres proceeding from the stem. These fibres, 

 which are vessels, by branching out in various directions, 

 form a kind of net-work, which represents the skeleton of the 

 leaf, and whose meshes are filled up with cellular tissue, which 

 is more or less abundant, and which derives its origin from 

 the herbaceous integument of the stem. 



The upper surface of the leaf is covered with a closely 

 adhering epidermis, and has but few cortical pores : the under 

 surface is also covered with an epidermis, has a greater num- 

 ber of small pores, which are the orifices of the internal 

 vessels of the vegetable. It is particularly by this under 

 surface, that leaves absorb the fluids, that are exhaled from 

 the surface of the earth, and that are diffused through the 

 atmosphere. 



Nerves of leaves, properly so called, are very prominent : 

 veins are less prominent. 



The nerves are bundles of porous vessels, of spirals, and of 

 false spirals, enveloped in a certain quantity of cellular tissue. 

 (See Plate, 11, and Explanation.) The disposition of nerves 

 in leaves deserves the greatest attention. In most of the mono- 

 cotyledons, they are almost always simple, and often parallel 

 to each other. 



