454 POPULAR BOTANY. 
1 he constituent parts of the plants are, in general, roots, stem, leaves, 
calyx, corolla, germ, pistil, filaments, fruit, and seed. Besides these, 
many plants are found to have other organic parts which, however, 
would be too numerous to mention in this place. Every one of these 
organs has its certain function to fulfil. The root, for instance, serves 
simultaneously as an anchor to fasten the plant to the ground, and, at 
the same time, to absorb nourishment therefrom. In the tender stage 
the plant must depend on the root only for its support. Boots and stem 
always grow in their due proportion ; the former, however, must always 
be a little in advance, in order to fulfil its functions as the anchor, as 
well as supporter. The stem serves as the medium of communication 
between the root and the other parts of the p 7 ant. The leaves absorb 
and decompose a portion of the carbonic acid gas from the atmosphere. 
The calyx affords protection for the developing blossom. The corolla 
envelopes the delicate germ, pistil and filaments. The germ is the 
nucleus of the future fruit ; the fruit contains the seed, which latter, for 
the most part, furnishes the common means for future propagation. 
It would become too tedious here to describe all the functions of the 
parts above enumerated ; I will therefore confine myself, on this 
occasion, to a few hints on the different ways and means cf which 
Nature makes use for the distribution of plants over the surface of our 
globe. Although plants are not endowed by Nature with voluntary 
motion, still they will travel by degrees over the whole earth. One of 
the most common means for this effect is the wind. The seeds of many 
families of plants, as for instance, ferns, mosses and lichens, are so ex- 
ceedingly dust-like that they are taken up by the wind in large quanti- 
ties and transported to a distance of hundreds, nay, thousands of miles. 
At certain seasons the atmosphere is filled with these invisible atoms 
by the million, and they are kept afloat until they come in contact with 
some object to which they adhere, and under favourable conditions they 
germinate and grow. This fact is easily observable on the shady side 
of brown-stone houses. Where there is sufficient moisture to germinate 
the plants, there we find a green substance accumulating particularly 
about the steps, which is nothing else than the young plants of mosses, 
lichens or ferns. 
The seeds of many other plants are covered at the apex with a hair- 
like tuft — pappus — for instance, the thistle, dandelion, aster, &c. This 
renders such seeds also binyant and susceptible of being easily floated 
through the air, yet not to so great a distance as in the former case. In 
other cases the seeds are enveloped in a woolly substance, as the cotton, 
willow, poplar, asclepias, &c, and they are conveyed away in the same 
manner as the -former. Some seeds are provided with membranaceous 
and wing-like appendages, as the maple, ash, elm, pine, &c. These are 
also carried away by the same agency of the wind, to a shorter distance. 
Another ver} 7 important agent for the distribution of seeds is water. 
