Cone Bearing Evergreens
( Originally Published 1927 )
The cone-bearers, or conifers, are a distinct race that we commonly call evergreens. They include pines, hemlocks, spruces, firs, sequoias, cypresses, cedars, and junipers. Besides these, the tamaracks and the bald cypress must be included, although their leaves are shed in the autumn. The term "evergreen" applies equally well to magnolias, laurels, and many oaks. Birches and alders and magnolias bear cone-like fruits. Notwithstanding such exceptions, the cone-bearing trees are mostly evergreen, and their family traits are so strongly marked that even the be-ginner in tree study eliminates the exceptional instances early in his studies.
The pines and their relatives in the coniferous group are an ancient race, composed of proud old "first families." Along the shores of the Silurian seas they stood up, straight and tall, their only companions that stood erect, the giant horse-tails and tree ferns. This was long before modern tree families had any existence. There were no broadleaved trees. In the coal measures are found the mummied remains of these prehistoric conifers. The cycads in the Everglades of Florida are some of their surviving representatives. These are facing extinction, and the conifers, too, are declining. They had reached their prime as a race when the broad-leaved trees appeared upon the earth. The vigor of the new race enabled it to seize the richest, well-watered regions. They drove the conifers to seek the swamps, the exposed seacoasts, the barren and rocky mountain slopes. Man has ruthlessly destroyed for timber the coniferous forests of this country and much of the territory denuded by the axe is either devoted to agriculture or has been seized by broad-leaved species of trees, more tenacious of life and with seeds more quick and sure to germinate than those of the conifers. The time is not far distant, geologically speaking, when this ancient and declining family of trees will exist only as man fosters it by cultivation.
The conifers have resinous wood, with stiff, needle-like or scale-like leaves, and inconspicuous flowers of two sorts, borne in clusters like catkins. The pistillate catkin matures into a woody cone made of overlapping scales attached to a central stem. On each scale are borne one or more winged seeds.
The one character which is constant in the whole coniferous group and sets it apart from the rest of the plant kingdom, is expressed in the name Gymnosperm, applied to this botanical grand division. It means "naked seed." There is no ovary in the flower. The naked ovules are borne on the scales of the fertile spike or catkin, which is held apart and erect in blossoming time. They are pollinated by the wind, which sifts them with golden pollen dust, abundant in the staminate catkins clustered on the same tree. Contact of pollen grains and naked ovules is followed by their coalescence—the "setting of seeds."
The distinguishing trait of the higher plants that form the grand division known as Angiosperms, is that the ovules are borne in a closed ovary, and the pollen lodges on the end of a stigma. "Pollen tubes" grow down through the long style, finally reach the hidden ovule, and seed is set. This complicated process is found in the majority of flowers one studies in botany classes. Gymnosperms, and the still lower groups of flowerless ferns and mosses, are merely glanced at by amateur botanists. The more primitive plant forms are too difficult for beginners.
The habit of the conifers is a character upon which we may depend. With rare exceptions, there is a central shaft, "the leader," and short horizontal branches in whorls forming platforms. The side branches, also whorled, are generally flattened into a horizontal spray. The leaves are narrow, needle-like, or scale-like, and waxy or resinous. The tough fibre of the wood enables the conifers to resist damage by wind and by ice. Snowflakes sift to the ground instead of accumulating upon the branches and breaking them by their cumulative weight. The wind, which pollinated the fertile flowers of coniferous forests long before nectar-gathering insects came upon the earth, is the harvester of their seeds. It scatters them far and wide; each seed has a wing that adapts it to Iong journeys in front of a gale.
The resinous sap that courses through the veins of coniferous wood seals up the bark, leaves, and cones against the invasion of enemies, and acts as an antiseptic dressing for wounds. Without these special adaptations to a life of hardship, the conifers would never have held their own as they have done. They inhabit regions where conditions discourage all but a few of the broad-leaved trees.