INTRODUCTION. 



Among the plants which constitute the ordinary covering of the ground, whether 

 that covering be one of forests, peopled by vegetable giants, or of the herbage and 

 small herbaceous plants that clothe the open country, we observe that the greater 

 number — at least of those which ordinarily force themselves on our notice — have 

 certain obvious organs or parts: namely, a root by which they are fixed in the 

 ground, and through which they derive their nourishment from the fluids of 

 the soil ; a stem or axis developed, in ordinary cases, above ground ; leaves 

 which clothe that stem, and in which the crude food absorbed by the roots and 

 transmitted through the stem is exposed to the influence of solar light and of the 

 air ; and, finally, special modifications of leaf buds called /loioers, in which seeds 

 are originated and brought to maturity. These seeds, falling from the parent plant, 

 endowed with an independent life under whose influence they germinate, attract 

 food from surrounding mineral matter ; digest it ; organize it, that is, convert it 

 from dead substance into living substance ; form new parts or organs from this 

 prepared matter ; and, finally, grow into vegetables, having parts similar to those of 

 the parent plant, and similarly arranged. 



This is the usual course of vegetation : seeds develope roots, stems, and leafy 

 branches ; the latter at maturity bear flowers, producing similar seeds, destined to go 

 through a like course ; and so on, from one vegetable generation to another. But, 

 with a perfect agreement among seed-bearing plants in the end proposed and 

 attained, there is an endless variety of minor modifications through which the end 

 is compassed. All degrees of modification exist between the simplest and most 

 complicated digestive organs ; in some, the root, stem, and leaves are so blended 

 too-ether, that we lose the notion of distinct organs, and in others the leaves ai'e 

 reduced to scales or spines, while the stem and branches are expanded and become 

 not merely leaf-like, but actually discharge the functions of leaves. In the repro- 

 ductive organs or flowers, too, we find equal variety ; from the most elaborate 

 and often gorgeous structures to the simplest and plainest, till at last Ave arrive at 

 flowers, whose organization is so low that not only have calyx and corolla disap- 

 peared, but the very seed-vessel itself is reduced to an open scale or is wholly 

 absent. Yet in all these modifications it is merely the means that are varied ; the 



VOL. m. ART. 4. B 



