83. Plant Life defined. The vital principle in the plant or its life is known only by its effects. In the animal these effects are, in kind, twofold, indicating two kinds of life, the organic and the nervous life. In the plant the latter kind is wanting, and the sum of its vital phenomena is popularly expressed in the one word, vegetation.
84. STAGES OF PLANT LIFE. The successive phenomena of vegetation are germination, growth, flowering, fruit-bearing, sleeping, dying; and we may add along with these, absorption, digestion, secretion. The development of every plant, herb or tree, commences with the minute embryo, advances throngh a continual series of transformations, with a gradual increase of stature, to its appointed limit.
85. The Life of the plast is a beography. Its fans is never permament, but changing like a series of dissolving views. The picture which it presents to the eye to-day differs, perhaps imperoeptibly, from that of yesterday. But let the views be successively sketched when in sprouts from the seed in spring, when clothed in its leafy robes, when crowned with flowers, when laden with ripe fruit, and when dead or dormant in winter-and the pictures differ as widely as those of species the most opposite.
86. The term or period of plant life varies between wide extremes, from the epherneral mushroom to the church-yard yew, whose years are reckoned by thousands. The term of life for each species is, of course, mainly dependent on its own laws of growth, yet is often modified by the climate and seasons. The the castor oil bean (Ricinus) is an annual herb in the Northern States, a shrab in the Southern, and a tree forty feet in bright in its native India.
If it occur within the first or second rear of the fife of the plant it generally proves the fatal event. In all Other cases it is either preceded or followed by a state of needful repose. Now if flowering be prevented by nipping the buds, the tender annual may become perennial, as in the florits's tree=mignionette.
88. We distinguish plants, as to their teem of life, into the an-nual (1) the biennial (2), and the perennial (4).
89. An Annual Herb is a plant whose entire life is limited to a single season. It germinates from the seed in spring, attins its growth, blossoms, bears fruit, and dies in autumn, as the flax, corn, morning-glory.
90. A Biennial Herb a plant which germinates and vegetates, bearing leaves only the first season, blossoms, bears fruit, and dies the second, as the beet and turnip Wheat, rye, & c, are annual plants, but when sown in autumn they have the habit of biennials, in consequence of the prevention of flowering by the sudden cold.
91. MONOCARPIC HERBS. The century plant (Agave), the taliport palm, etc, are so called. They vegetate, bearing leaves only, for many years, accumulating materials and strength for one mighty effort in fructification, which being accomplished, they die. But althrough the vital principle is extenguished in the parent, it surivives multipled a thousand fold fold in the seed.
92. Perennial Plants are such as have as indefinite duration of life, usually of many years. They may be either herbaceous or woody.
93. Herbaceous Perennials, or perennial herbs, are plants whose parts are annual above ground and perennial below. In other words, their roots or subterranean stems live from year to year, sending up annually in spring flowering shoots, which perish after they have ripened their fruit in autumn; as the lily, dandelion, hop.
94. Woody perennials usually vegetate several years, and attain well nigh their ordinary stature before flowering; thenceforward they fructify annually, resting or sleeping in winter. They are known as trees, shrubs, bushes and undershrubs - distinctions founded on size alone.
95. A shrub is a diminutive tree, limited to eighteen or twenty feet in stature, and generally dividing into branches at or near the surface of the ground (alder, quince). If the woody plant be limited to a still lower growth, say about the human stature, it is called a bush, (snow-ball, Andromeda.) If still smaller, it is an undershrub (whortleberry).
96. A tree is understood to attain to a height many times greater than the human stature, with a permanent woody stem, whose lower part, the trunk, is unbranched.
97. Longevity of trees. Some trees live only a few years, rapidly attaining their growth and rapidly decaying, as the peach; others have a longevity exceeding the age of man, and some species outlive many generations.
98. The age of a tree may be estimated by the number of wood-circles or rings seen in a cross section of the trunk (§ 667), each ring being (very generally) an annual growth.
99. Examples. The known age of an elm, as stated by De Candolle, was 335 years; of a larch, 576; a chestnut, 600; an orange, 630; oaks, from 810 to 1500; yews, 1214 to 2820.
100. Adanson estimated the age of the baobabs of Africa at 5000 years, Livingston reduces it to 1800. The yew trees of Britain, as described by Balfour, are of wonderful longevity. One in Bradburn church-yard, Kent, is 3000 years old, and the great yew at Hedsor, Bucks, twenty-seven feet in diameter, has vegetated 3200 years.
101. Magnitude. At the first establishment of Dartmouth College, a pine tree was felled upon the college plain which measured 210 feet in height. In the Ohio Valley the red maple attains a girth of 20 feet, the tulip-tree of 30, and the sycamore of more than 60. But the monarch tree of the world is the Sequoya gigantea - the California pine. One which had fallen measured 31 feet in diameter, and 363 feet in length. Among those yet standing are some of still greater dimensions, as beautiful in form as they are sublime in height, the growth (as estimated by the wood-circles) of more than 3000 years.
102. Trees are again distinguished as decidous and evergreen - the former losing their foliage in autumn and remaining naked until the following spring; the latter retaining their leaves and verdure throughout all seasons. The fir tribe (Coniferae) includes nearly all the evergreens of the North; those of the South are far more numerous in kind, e. g., the magnolias, the live-oaks, holly, cherry, palmetto, etc.