QUANTITIES OF CARBON DIOXIDE EVOLVED. 399 



the plants can respire in a normal atmosphere, and we are at the same time able 

 to determine the amount of carbon dioxide respired from time to time, without the 

 plants themselves being thereby destroyed. 



In the course of very numerous investigations on the respiration of plants, various 

 observers have made use of several different kinds of apparatus, which however 

 mostly do not offer the advantages mentioned, and do not allow of a long-oontinued 

 normal growth of the plants in the apparatus. 



It would carry us much too far for my purpose to quote even abstracts of the 

 experiments, but the general results obtained from the numerous experiments m^y 

 well be referred to. 



With respect to the absolute magnitude of the respiration — i. e. the q^aantity of 

 carbon dioxide which is expired by a definite weight or volume of plant-substance 

 — Garreau found for example that twelve buds of Syringa vulgaris, which when 

 dried at iio°C. weighed two grams, exhaled 70 c.cm. of carbon dioxide in twenty- 

 four hours, the leaves having unfolded during the experiment. In the same way five 

 buds of ^sculus maarosiachya, the dry weight of which amounted to ts-Ss gram, 

 produced 45 c.cm. in twenty-four hours, the leaves having unfolded im this case also. 

 Garreau further sowed seeds in fine sand, moistened with rain-water, and then 

 brought the seedlings, deprived of the seed-coats, under the receiver, where the 

 carbon dioxide exhaled at 16° C. was determined. Seedlings of Papaver somniferum, 

 which weighed 0*45 gram when dried subsequently, evolved 55 c.cm, of carboii 

 dioxide in twenty-four hours; and in the same way seedlings of Sinapis nigra, 

 the dry weight of which was 0-55 gram, evolved 32 c.cm. of carbon dioxide in 

 twenty-four hours. 



Charles Lory investigated phanerogamous parasites — Orobanche, Lathraa, and 

 the humus plant Neottia, which contains small quantities of chlorophyll, and found 

 that they are always taking up oxygen and exhaling carbon dioxide. At i8°C. 

 Orobanche Teucrii in full bloom used up its own volume of oxygen in thirty-six hours 

 ■ — i. e. 4.2 c.cm. per one gram of substance, correspoiading to a loss of 3 '2 6 mgr. 

 of carbon. 



The activity of the respiration — i. e. the carbon dioxide exhaled in a given time 

 by a certain weight or volume of living plant- substance — varies according to the 

 state of development, the activity of growth, and according to the vitality generally of 

 the part of the plant concerned. At the commencement of the germination of seeds 

 and buds, therefore, but little carbon dioxide is at first disengaged : its quantity 

 increases with progressive development, to diminish again later, when the material 

 for respiration in the interior of the organ begins to fail. The activity of respiration, 

 in fact, does not depend upon the total mass of substance which may- happen 

 to be present in the plant, but upon how large a quantity of it is being 

 immediately employed, in growth and other vital processes. When such material 

 begins to fail, the energy of respiration diminishes also. 



Sincp not only growth but also all other functions which depend upon respira- 

 tion become more energetic as the temperature rises up to the optimum, so also 

 Ihe carbon dioxide exhaled increases, other relations being the same, as the temper- 

 ature rises, reaching its maximum at the optimum temperature. 



The energy of respiration of an organ also varies according to its physiological 



