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 the sepals of the calyx, the outer 

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

 more abrupt, they pass into the delicate and highly colored petals 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 ccnti-al organs, 

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

 imited edges being yet discernible. 



26. "V^Tien tlie flower has accomplished its brief but unpor- 

 taut office 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. Tliis being accom- 

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

 or, if not, it continues to put forth new branches, fr6m other 

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

 flowers and fntit the following year. 



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

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

 sible to contemplate it, without admiring that simplicity of design in the midst of 

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

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

 organic form, of which the leaf is tlie tj-pe. The lamina, or blade, in various 

 stages of transition, constitutes the several organs of fmctification, 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 diiferent parts, however various in appearance, all constnicted of the 

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

 framework of veins, a Jleshy substance filling up the interstices, and a ciUicle, or 

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

 ducts, and air-ifesseh, all of which may be traced through the foot-stalk into the 

 stem, where they equally exist, — this part of the leaf being 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, woodij tissue, vasi/orm tissue, 

 vascular tissue, and laticifcrous tissue. 



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



