or plants with a single seed leaf, have been for hundreds of years the two great classes into which all angiospermous flowering plants are divided.
Our general view of all the flowering plants may be summarized then as follows:
1. Gymnosperms, or naked seeded plants, include all cone-bearing plants, mostly evergreen and always trees or shrubs. The pine is a familiar example.
2. Angiosperms, or inclosed seeded plants, include all other flowering plants of whatever kind. Divided into: (a) Monocotyledons. Sprouting with one seed leaf, and leaves practically always parallel-veined. Parts of the flower in threes or multiples of three. Familiar examples are corn, grass, sugar-cane, palms, cannas, and lily of the valley ([Figures 82-85]). (b) Dicotyledons. Sprouting with two seed leaves, and the leaves practically always netted-veined. Parts of the flower in fours or fives or multiples of these numbers. Includes all the remaining flowering plants and is a larger group than the monocotyledons and the cone-bearing plants combined ([Figures 78-81]).
No matter from what part of the world a totally unfamiliar plant may come, it is always possible to decide into which one of these groups it belongs. That in itself tells us a good deal about its ancestors and its future, “places” it, in fact, in one of those major groups into which all plants are divided. No other characters that plants possess are so important in determining their true position in the scale of plant life as those we have briefly outlined. But merely to sort plants into these large groups does not tell us all we need to know about them. For all plants not only belong to monocotyledons, or dicotyledons, or gymnosperms, but also to smaller divisions of these groups. Just as white men are divided into Englishmen, Frenchmen, etc., so there is the greatest necessity of dividing our large plant groups into smaller and more precise categories.
Some of the chief subdivisions of these large groups have been decided upon the fact that a considerable number of plants in them have some character in common, not found in the remaining plants of the group. Among the monocotyledons, for instance, there is a large class of plants that have tiny flowers between dry, chaffy scales, bear no true petals or sepals, all wind pollinated and are all commonly, though incorrectly, called grasses. These include, strictly speaking, two groups; one, the true grasses in which the stem is mostly hollow and the fruit a grain, while the other, with solid stems and bearing achenes for fruits, are the sedges. The grasses form one family and the sedges another, but while they differ in the characters just mentioned they agree in having flowers of the same general type. Families of plants are thus groups of genera, placed together in the scheme of classification, because they are more like one another than like any other such group. Among the grasses, for instance, are corn, wheat, rice, bamboo, orchard grass, Kentucky blue grass, sugar cane, and hundreds of others, all belonging to different genera, but all those genera grouped into a single family because of their generally similar flowers. Just as the Kentucky blue grass has a generic name (Poa) and a specific one (pratensis), the families of plants must also bear names, usually derived from the generic name of one of the chief genera in it. Because Poa is a large and important genus of the grasses, the family is named after it, with the addition of ceæ. Poaceæ is thus the family name of all the grasses. Among the sedges one of the commonest genera is Cyperus, including many species of the galingale or earth almond. From this genus the sedge family has been named Cyperaceæ ([Figure 87]). So the rose family is the Rosaceæ, the violet family is Violaceæ, and so on through all the three hundred or more families which contain all the flowering plants so far discovered. Going back for a moment to the Poaceæ and Cyperaceæ, the fact that these two large families are different from each other, but have some characters in common, fixes them as both belonging to one order. Orders are thus groups of one or more plant families, all differing one from another, but obviously related and having some characters in common. The order containing the grasses and sedges is named for one of the families in it with the ending ales. Thus Poales include Poaceæ and Cyperaceæ. Rosales include Rosaceæ and several families.
In other words, individual plants are grouped in species, species into genera, genera into families, and families into orders. These orders are themselves grouped into still larger divisions; there are, for instance, twelve orders comprising all the monocotyledons, and about twenty orders comprising all the dicotyledons. Once we have decided that any plant is a monocotyledon or a dicotyledon, our next step should be as to which order it belongs, then its family, its genus, and finally its species. Needless to say, such studies are necessarily of a technical nature, and while the details of them lie outside the scope of this book, the general plan or scheme of flowering plant classification is as we have outlined it above.
This scheme of plant classification has been developed not only for our convenience in sorting plants into definite categories, but more important still to show, if possible, the relationships, and particularly the development from the simplest to the most complex types of plant life. Thus the monocotyledons begin with the cat-tails, which have mere bristles for calyx and corolla, and lead by infinite gradations to the showy and highly complex orchids, which are considered the climax of the monocotyledonous families. While no general account of the plant families can be attempted here, some of the more interesting in both the monocotyledonous and dicotyledonous groups will be briefly discussed.