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. SUB-KINGDOM I. PROTOPHYTES. The name Protophytes (_Protophyta_) has been applied to a large number of simple plants, which differ a good deal among themselves. Some of them differ strikingly from the higher plants, and resemble so remarkably certain low forms of animal life as to be quite indistinguishable from them, at least in certain stages. Indeed, there are certain forms that are quite as much animal as vegetable in their attributes, and must be regarded as connecting the two kingdoms. Such forms are the slime moulds (Fig. 5), _Euglena_ (Fig. 9), _Volvox_ (Fig. 10), and others.