52 Prof. Asa Gray on Sequoia and its History. growths is also insignificant, and out of proportion to the car-bonic acid evolved. We must therefore in this case decline to accept the root-absorption hypothesis, and admit that the carbonic acid has arisen as a result of the cell-growth in the plant. Passing to the chlorophyl-bearing plants, we find that in the Phanerogamia it is only the green parts that at any time exhale oxygen, and then only under the influence of sunshine. The Other parts of the plant above the ground that are not green, viz. the stem, twigs, flowers, &c., are at all times, day and night, exhaling carbonic acid, ^he whole history of the plant, from the time the seed is planted till its death, is a continuous story of oxidation, except when sunlight is falling on the leaves. The seed is put into the ground ; and during germination oxygen is absorbed and carbonic acid exhaled. If the seedling is kept in the dark, oxygen is never exhaled, only carbonic acid, and the plant not only grows, but all visible structures, except flowers, are formed in a rudimentary condition. In the light, the growth during the night time is attended by the evolution of carbonic acid, while during the daytime the bark of the stem and branches is throwing off carbonic acid. When flowers and seeds form, the evolution of carbonic acid attending this highest act of which the plant is capable is often greater than that produced at any time in many animals. Every thing in the history of plants therefore tends to show that the evolution of their sti'uctures is inseparably attended by the formation of carbonic acid ; and it seems impossible, when we consider the evolution alone, to arrive at any other opinion than that already expressed — that all living things^ whether plant or animal^ absorb oxygen and evolve carbonic acid^ or some other oxidized substance^ as an essential condition of the evolution of their structures. College of the City of New York, Sept. 12tli, 1872. VII. — Sequoia and its History. By Professor AsA Gray, President of the American Association for the Advancement of Science*. The session being now happily inaugurated, yom* presiding officer of the last year has only one duty to perform before he suiTenders his chair to his successor. If allowed to borrow a simile from the language of my own profession, I might liken * An addi'ess delivered at the meetiu'r held at Dubuque, Iowa, August 1872. >i ' c
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