156 BOTANY. 



3d, Solid bulbs, the coats of which are so compact and con- 

 founded, that they are indistinguishable, and seem formed of 

 a solid and homogeneous substance; this last however is 

 more properly called a cormus. 



TUBERCLES. 



This name is given to short and thickened portions of a 

 subterranean stem which holds in reserve the amidon destined 

 to nourish the shoot or shoots which spring from them, as 

 we see in the Potato and the Orchis. When small they are 

 termed tubercles. 



BULBILS. 



Small solid or scaly buds growing upon different parts of 

 the plant, and capable of a separate vegetation. 



LEAVES. 



Appendages of stems, generally membranous, plane, and 

 greenish, in which the vegetable juices (water charged with 

 carbonic acid) being put in relation with the fluids of the 

 atmosphere, undergo important modifications which render 

 them nutritive. Under the influence of the solar light, the 

 carbonic acid which issues either from the part absorbed 

 with the water, by the spongioli, or from the part absorbed 

 by the leaves, is decomposed ; the oxygen is exhaled ; the 

 carbon forms matter eminently combustible, such as lignine 

 or wood, saccharine, gum and amidon. This respiration of 

 leaves is accompanied by a very abundant aqueous exhala- 

 tion ; about two-thirds of the water absorbed by the roots. 



We must regard the leaves as formed by the expansion of 

 a collection or bundle of vessels, which, in some measure, 

 compose their skeleton or veins ; the intervals left between 

 the veins are filled by a substance analogous with the herba- 

 ceous envelope, parenchyma, which is moulded around these 

 veins as the soft parts of animals around the bony system. 

 It is evident that the general form of the leaf depends upon 

 the disposition of the principal veins, and that the modifica- 

 tions exhibited by the edge of the same leaf depend upon the 

 disposition of the secondary veins, the tertiary, &c. When- 

 ever the principal or secondary veins are sufficiently near 



