In studying man we are able not only to divide him into such broad divisions as white, black, and yellow races, but due to their particular country or mode of life there are scores of racial subdivisions of these larger categories that everyone recognizes. Such differences are often based on stature, shape of head, mental characters and many others, but those still finer shades of difference between, for instance, a Connecticut Yankee and a plantation owner in the South, are, while noted by everyone, very difficult to accurately describe.
In attempting to find such major differences in plants, some structural character that would set off one large group of plants from every other group, the botanist has a harder task than the person studying man. For all those differences of language and mentality that make up such a large part of our common knowledge of the different peoples of the earth are characters that are foreign to plants. We are thus thrown back on structure as the chief way in which plants differ, and because their reproductive organs are their most important ones, and therefore least likely to vary, it is upon certain characters of these organs that all flowering plants have been divided.
In the chapter on “How Plants Produce Their Young,” we found that most flowering plants have their ovules in an ovary which, after fertilization, develop into fruit and seed. But some plants, while they have ovules, only bear them naked or between scales, never inclosed in an ovary. This is true in all pines, spruces, hemlocks, and all the host of their generally evergreen relatives. Such trees bear cones, between the scales of which are perfectly naked ovules that develop into seeds ([Figure 77]) that have never been hidden in an ovary, as have the vast majority of the seeds of other plants ([Figure 53]). These naked-seeded plants are known as gymnosperms or literally gymnos, naked, and sperma, seed, and comprise all the cone-bearing trees in the world, the larger part of which are always evergreen. In some past ages such trees made up the bulk of vegetation of the earth, but at present they are much reduced in numbers. Familiar examples of these Coniferæ, or cone-bearing trees, are larch, spruce, fir, pine, hemlock, juniper, and yew.
Most of these are evergreen, which does not, of course, mean that they bear the same leaves always, but that only a few drop off at a time and are so constantly renewed that the tree is actually ever green.
All other flowering plants always bear their ovules in an ovary and, because of this fact, are called angiosperms, literally angeion, a vessel, and sperma, seed. These inclosed seeded plants comprise the great bulk of the vegetation of the earth to-day. So far as the temperate zone is concerned, nearly all of them drop their leaves in the fall, and the trees belonging to the angiosperms are thus said to be deciduous trees.