20 PLAN OF VEGETATION. 



below the flower, become simple bracts, still retaining every essential mark of a 

 leaf. Next, by an easy gradation, they appear in tlie sq)als of the calyx, the outer 

 envelope of the flower, still essentially the same. Then, by a transition rather 

 more abrupt, they pass into the delicate and highly colored petcds of the corolla, 

 retaining still the form and organization of the leaf. To the petals next succeed 

 those slender organs called stamens, known to be undeveloped leaves from the 

 fact of their being often converted into petals. Lastly, those two central organs, 

 termed pistils, are each the result of the infolding of a leaf, the midrib and the 

 united edges being yet discernible. 



26. When the flower has accompHshed its brief but impor- 

 tant ofiice in reproduction, its deciduous parts fall away, and 

 the remaining energies of the plant are directed to the devel- 

 opment of the germ into the perfect fruit. This being accom- 

 plished, the whole plant speedily perishes, if it be an annual, 

 or, if not, it continues to put forth new branches, from other 

 growing points, which, in their turn, are to be terminated by 

 flowers and fruit the following year. 



a. Such is a very brief outline of the plan of vegetation, or the process of nature 

 in the germination, growth, fructification, and decay of plants. And it is impos- 

 sible to contemplate it, vsithout admiring that simplicity of design in the midst of 

 the most diversified results which every where characterizes the works of Grod. 

 Every part of the vegetable fabric may be ultimately traced to one elementary- 

 organic form, of which the leaf is the type. The lamina, or blade, in various 

 stages of transition, constitutes the several organs of fructification, while the 

 united bases of all the leaves constitute the axis itself. 



27. When we more minutely examine the internal organization of plants, we 

 find their diff'erent parts, however various in appearance, all constructed of the 

 same materials. The leaf, for example, consists of a foot-stalk prolonged into a 

 framework of veins, a fleshy substance filling up the interstices, and a cuticle, or 

 skin, covering the whole. Now this framework is composed of woody fibre, aque- 

 ducts, and air-vessels, all of wliich may be traced through the foot-stalk into the 

 stem, where they equally exist, — this part of the leaf bemg only a prolongation 

 of the stem. The fleshy substance is of the same nature with the pith of the 

 stem, or the pulp of the fruit ; and, finally, the cuticle corresponds exactly to the 

 thin covering of the newly formed branches, of the various parts of the flower, 

 and even of the roots. # 



a. These several kinds of structure, of which the various 

 organs are composed, are called the elementary tissues. They 

 are five in number ; — cellular tissue, woody tissue, vasiform tissue, 

 vascular tissue, and laticiferous tissue. 



28. The chemical basis of the vegetable tissues is proved by 



