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 



