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 the 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 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 accomplished its brief but impor- 
tant 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. 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, 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 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 different 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 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, woody tissue, vasiform - 
vascular tissue, and laticiferous tissue. 
28. The chemical basis of the vegetable tissues is proved Oye ae 
