114- 



HISTORY OF THE VEGETABLE KINGDOIW. 



atmosphere containing but one-fourth of its 

 vohime of the same gas, they lived ten days, 

 ajid augmented their weight hy five grains. 

 Lastly, the mean augmentation in vireight of 

 such as were placed in an atmosphere of common 

 air, containing one-twelfth part of carhonic acid 

 gas, was eleven grains. This experiment was 

 repeated frequently, and was found to yield a 

 uniform result; the plants always succeeding 

 better than in pure atmospheric air. Carbonic 

 acid gas, therefore, is of gi-eat utility to the 

 growth of plants vegetating in the sun, as applied 

 to the leaves and branches, and whatever in- 

 creases the proportion of this gas in their atmo 

 sphere, at least -within a given degree, forwards 

 vegetation. 



But the result was not the same when the 

 plant was placed in the shade ; the smallest dose 

 of carbonic acid gas, in addition to that of the 

 atmospheric air, being then prejudicial to vege- 

 tation. This appears from the following ex- 

 periments: Plants kept in the shade, and placed 

 in an atmosphere containing one-fourth of its 

 volume of carbonic acid gas, died on tlie sixth 

 day ; and when the atmosphere contained only 

 one-twelfth of its volume of this gas, they lived 

 indeed ten days, but weighed only three grains, 

 while those in pure atmospheric air weighed 

 five grains. Carbonic acid gas, therefore, as 

 applied to the leaves and branches of plants, is 

 prejudicial to their vegetation in the shade, if 

 administered in a proportion beyond that in 

 which it exists in atmospheric air. This may 

 be readily accounted for from the now ascer- 

 tained modes in which plants feed and respire. 



In the shade, plants absorb oxygen, and throw 

 out carbonic acid gas, or perform a function 

 nearly allied to the respiration of animals. In 

 sunshine they absorb carbonic acid, and give out 

 oxygen, or perform an action somewhat analo- 

 gous to digestion. 



But carbonic acid gas is also beneficia] to the 

 growth of the plant, when applied to the root. 

 This Saussure ascertained by experiment also. 

 Two boards, pierced with a number of holes, 

 were made to float in two vessels filled, one with 

 distilled water, and the other with water im- 

 pregnated with carbonic acid gas. On each of 

 these boards was placed a number of peas that 

 had been lately made to germinate in distilled 

 water. Their radicles at the commencement of 

 the experiment were two lines and a half long. 

 At the end of ten days, the roots in contact with 

 the distilled water were longer by five inches, 

 than those in contact with the acidulated water; 

 and the stalks and leaves were developed in the 

 same proportion. But at the end of a month 

 the plants vegetating in the acidulated water, 

 had acquired the same dimensions as the others, 

 and at the end of six weeks had considerably 

 surpassed them. It follows, therefore, that car- 



bonic acid gas as applied to the roots of plants, 

 is also beneficial to their growth, at least, in the 

 more advanced stages of vegetation. 



Oxygen. As oxygen is essential to the com- 

 mencement and progress of germination; so also 

 it is essential to the progress of vegetation. This 

 is clearly proved by the following expei-iments 

 of Saussure : Having pulled up some young 

 plants of the horse-chestnut, furnished with 

 their leaves, and weighing about 460 grains, he 

 introduced their roots, which were nearly a foot 

 in length, into receivers of about sixty cubic 

 inches in capacity, and luted the base of the 

 stem to the neck of the receiver. Into one of 

 the receivers, each of which contained a quan- 

 tity of distUled water, he introduced twenty- 

 eight cubic inches of nitrogen, which was in 

 contact with the upper part of the root, while 

 the under part was immersed in water. Into 

 another he introduced an equal quantity of hy- 

 drogen; and into a third an equal quantity of 

 carbonic acid. The plant, whose root was in 

 contact with the carbonic acid, died in the course 

 of eight days : the others lived a fortnight, but 

 had not diminished the volume of their atmos- 

 phere. But plants which were placed at the same 

 time in a similar apparatus, furnished with at- 

 mospheric air, gave a very different result; for 

 at the end of three weeks, when the experiment 

 was stopped, they were still fresh and vigorous, 

 and the volume of their atmosphere was dimin- 

 ished. It is obvious, then, that the presence of 

 oxygen is beneficial to the growth of the vege- 

 table, at least, as applied to the root; because 

 that is the only principle which had access to 

 the root in the last experiment, which had not 

 access to it in the former. 



But oxygen is beneficial to vegetation, as ap- 

 plied also to the other parts of the plant as well 

 as to the root. Branches of woody plants taken 

 in the spring, immediately before the expansion 

 of the bud, and enclosed in receivers filled with 

 common air, together with a small quantity of 

 water to supply them with moisture, developed 

 their leaves as if attached to the parent plant. 

 And this development was effected solely by 

 means of the oxygen contained in the receiver; 

 for in mediums deprived of oxj^gen, no deve- 

 lopment took place. The presence of oxygen, 

 therefore, is necessary to the development of the 

 leaves. 



But it is necessary also to the development of the 

 flower and fruit. The flower-bud will not expand 

 if confined in an atmosphere deprived of oxygen; 

 nor wUl the fruit ripen. Flower buds confined in 

 an atmosphere of pure nitrogen, faded without 

 expanding. A bunch of unripe grapes introduced 

 into a globe of glass, which was luted by its orifice 

 to the bough, and exposed to the sun, ripened 

 without eff'ecting any material alteration in its 

 atmosphere. But when a bunch was placed in 



