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For the sake of convenience it is desirable to collect into groups such plants as are evidently related; but as our knowledge of many forms is still very imperfect, any classification we may adopt must be to a great extent only provisional, and subject to change at any time, as new forms are discovered or others become better understood.

The following general divisions are usually accepted: I. Sub-kingdom (or Branch); II. Class; III. Order; IV. Family; V. Genus; VI. Species.

To illustrate: The white pine belongs to the highest great division (sub-kingdom) of the plant kingdom. The plants of this division all produce seeds, and hence are called “spermaphytes” (“seed plants”). They may be divided into two groups (classes), distinguished by certain peculiarities in the flowers and seeds. These are named respectively “gymnosperms” and “angiosperms,” and to the first our plant belongs. The gymnosperms may be further divided into several subordinate groups (orders), one of which, the conifers, or cone-bearing evergreens, includes our plant. This order includes several families, among them the fir family (Abietineæ), including the pines and firs. Of the sub-divisions (genera, sing. genus) of the fir family, one of the most familiar is the genus Pinus, which embraces all the true pines. Comparing different kinds of pines, we find that they differ in the form of the cones, arrangement of the leaves, and other minor particulars. The form we have selected differs from all other native forms in its cones, and also in having the leaves in fives, instead of twos or threes, as in most other kinds. Therefore to distinguish the white pine from all other pines, it is given a “specific” name, strobus.

The following table will show more plainly what is meant:

Sub-kingdom,

Spermaphyta. Includes all spermaphytes, or seed plants. Class, Gymnospermæ. All naked-seeded plants. Order, Coniferæ. All cone-bearing evergreens. Family, Abietineæ. Firs, Pines, etc. Genus, Pinus. Pines. Species, Strobus. White Pine.