Fig. 78.—Illustrations of gymnosperms. A, fruiting leaf of a cycad (Cycas), with macrosporangia (ovules) (ov.), × ¼. B, leaf of Gingko, × ½. C, branch of hemlock (Tsuga), with a ripe cone, × 1. D, red cedar (Juniperus), × 1. E, Arbor-vitæ (Thuja), × 1.
The spore-bearing leaves usually form cones, recalling somewhat in structure those of the horse-tails, but one of the commonest cultivated species (Cycas revoluta) bears the ovules, which are very large, upon leaves that are in shape much like the ordinary ones ([Fig. 78], A).
Of the conifers, there are numerous familiar forms, including all our common evergreen trees. There are two sub-orders,—the true conifers and the yews. In the latter there is no true cone, but the ovules are borne singly at the end of a branch, and the seed in the yew (Taxus) is surrounded by a bright red, fleshy integument. One species of yew, a low, straggling shrub, occurs sparingly in the northern states, and is the only representative of the group at the north. The European yew and the curious Japanese Gingko ([Fig. 78], B) are sometimes met with in cultivation.
Of the true conifers, there are a number of families, based on peculiarities in the leaves and cones. Some have needle-shaped leaves and dry cones like the firs, spruces, hemlock ([Fig. 78], C). Others have flattened, scale-like leaves, and more or less fleshy cones, like the red cedar ([Fig. 78], D) and Arbor-vitæ (E).
A few of the conifers, such as the tamarack or larch (Larix) and cypress (Taxodium), lose their leaves in the autumn, and are not, therefore, properly “evergreen.”
The conifers include some of the most valuable as well as the largest of trees. Their timber, especially that of some of the pines, is particularly valuable, and the resin of some of them is also of much commercial importance. Here belong the giant red-woods (Sequoia) of California, the largest of all American trees.
The joint firs are comparatively small plants, rarely if ever reaching the dimensions of trees. They are found in various parts of the world, but are few in number, and not at all likely to be met with by the ordinary student. Their flowers are rather more highly differentiated than those of the other gymnosperms, and are said to show some approach in structure to those of the angiosperms.