July 12, 1S77] 



NA TURE 



absorption of carbon-dioxide by plants growing under 

 different conditions as to soil and manures. He found that 

 a Helianthus which in twerity-four hours would, without 

 any manure, only decompose 2 c.c. of carbon-dioxide, 

 decomposed 182 c.c. in the same time when supplied with 

 manure containing nitrates and phosphates, 11 c.c. when 

 with nitrates without phosphates, and only from 3 to 5 c.c. 

 when manured with phosphates without nitrates. 



That the carbon-dioxide contained in the atmosphere is 

 sufficient for normal vegetation is proved by the abundant 

 growth of heath and other wild plants on sandy hills ; 

 and the numerous experiments on water-culture con- 

 clusively show that a plant may grow luxuriantly, and 

 store up an abundance of carbon, when supplied only 

 with mineral salts, in a solution which contains little or no 

 carbon-dioxide. 



Sachs speaks of it as an unquestionable fact, " that 

 most plants which contain chlorophyll (for instance, our 

 cereal crops, beans, tobacco, sun-flower, &c.) obtain tlie 

 entire quantity of their carbon by the decomposition of 

 atmospheric carbon-dioxide, and require for their nutri- 

 tion no other carbon-compound from without." He goes 

 on to say : " The compound of carbon originally present 

 on the earth is the dioxide, and the only abundantly 

 active cause of its decomposition and of the combination 

 of carbon with the elements of water is the cell containing 

 chlorophyll. Hence all compounds of carbon of this kind, 

 whether found in animals or in plant: or in the products 

 of their decomposition, are derived indirectly from the 

 organs of plants which contain chlorophyll." 



Dr. J. Boehm made direct experiments with seedlings 

 of scarlet-runner, growing them under glass shades, luted 

 with potass lye, in pots containing in some cases quartz 

 sand moistened with a nutritive solution, and in others 

 garden-soil rich in humus. The two sets were quite equal 

 in development and duration of life ; those in the garden 

 soil formed quite as little starch as those in the sand ; 

 and from this he concluded that the carbon dioxide 

 yielded by the garden soil had taken no share in the 

 growth of the plants, 



Liebig had, however, supposed that plants might owe 

 some part of their carbon to the carbon-compounds in 

 the soil, which were absorbed by their roots, and that 

 young plants especially drew their supply from this 

 source. He speaks of the effect of drought as checking 

 the supply of carbon-dioxide by the roots, and throwing 

 the plant exclusively upon that in the air. 



But the tendency of more recent investigations points 

 to the conclusion that the atmosphere and the parts of 

 plants living in it are solely concerned in the storing up 

 of the carbon of vegetation. 



We may pause for a moment to consider the amount 

 of the carbon so stored up. 



Liebig estimated that more than i,030 lbs. of carbon 

 may be harvested annually from a Morgen of surface — 

 somewhat less than two-thirds of an English acre. 



According to the estimates of Lawes and Gilbert, with 

 wheat for twenty years in succession on the same land 

 there was an actual yield of 2,500 lbs. of carbon, per acre, 

 per annum, where no organic carbon compounds were 

 added to the soil, and where these were added (in the 

 form of farm-yard manure) the actual yield in carbon was 

 less. With barley, for twenty years in succession, the 

 average annual yield was 2,088 lbs. of carbon per acre ; 

 and the indication is that some other crops, under similar 

 conditions, acquire even more. 



Estimates recently made of the forest growth in Ger- 

 many give as much as 2,700 lbs. In tropical climates 

 where vegetable growth is more luxuriant the amounts 

 are far greater ; and in the West India Islands as much 

 as from 2\ to 5 tons of carbon may be harvested per 

 acre in the crop of sugar-cane. 



With these large amounts of accumulation on the one 

 hand, we have, on the other, an atmosphere containing 



proportion as o'04 per 



carbon-dioxide in so small 

 cent. 



Then we have to bear in mind the large supplies of 

 caibon-dioxide within the pores especially ^of manured 

 soils, as determined by Boussingault, and at the disposal 

 of the roots of plants. Also the enormous quantity of 

 water taken up from the soil and passing through plants 

 during growth, probably at any rate more than 2CO 

 parts for every part of dry substance fixed, and the fact 

 that carbon-dioxide is present in all natural waters 

 would lead to the supposition that the roots would scarcely 

 either take it up to no purpose, or act as a filter to that 

 which constitutes so important a requirement of the plant. 



Dr. Moll ' has recently, by some interesting experi- 

 ments, made a contribution to the evidence which is re- 

 quired to answer the question — Can leaves decompose 

 the carbon-dioxide which is at the disposition of the 

 roots ? and argues that the proof that one part of the 

 plant — the leaf — takes up and decomposes carbon-di- 

 oxide, is no proof that it is not taken up in another part 

 — the root. 



He quotes the experiments of Sennebier and de Saus- 

 sure, but considers that they were not made quantitatively, 

 or with sufficient exactness to solve this problem. For 

 its elucidation he rests his methods upon Sach's theory, 

 that the starch in the chlorophyll grains must be con^ 

 sidered as the first visible product of the decomposition 

 of carbon-dioxide, and that therefore, according to him, 

 the presence or absence of starch in the leaves is the 

 crucial test of the decomposition or non-decomposition 

 of carbon-dioxide. In Dr. Moll's investigation of the 

 starch contents he used Sach's modification of Boehm's 

 method. 



Five sets of experiments were made to meet the dif- 

 ferent aspects of the question. 



In the first set glass shades were used, in one of which 

 the air was kept free from carbon-dioxide by being luted 

 with potass lye, while the other contained ordinary air, 

 or air with an excess of carbon-dioxide, and was luted 

 with water. The liquid lute was in porcelain dishes, 

 made with a round hole in the middle ; the central hole 

 and outer edge being deeply rimmed. The shades, of less 

 circumference than the dishes, were set in them, and 

 were furnished with tubular necks, into which smaller 

 tubes were fixed for the current of air to pass through, 

 and for other requirements of the experiments. The exit 

 tube of the shade in which the atmosphere was kept free 

 from carbon-dioxide was conducted through a test-tube 

 filled with pieces of pumice saturated with potass lye. 

 Preliminary experiments with etiolated plants, with a 

 watch glass containing baryta-water within the shade, 

 satisfied the author that he secured having air absolutely 

 free from carbon-dioxide under that luted with potass 

 lye ; and some early failures taught him how to regulate 

 the supply of carbon-dioxide and air in the other shade, 

 so as to grow plants as well-developed and healthy as 

 those in the open air. With thick-leaved plmts he found 

 that it v.'as necessary to add as much as 2 per cent, of 

 carbon-dioxide to a volume of air supplied to them of 

 about 2,500 c. c. daily, in order to satisfy their require- 

 ments for free growth. 



Experiments were made with plants of French bean, nas- 

 turtium, gourd, and sugar-beet, growing in the open air in 

 pots in good garden soil. From these was selected a leaf, 

 or the upper part of a stem with several leaves, still organi- 

 cally united with the parent plant, which was passed through 

 the hole in the porcelain dish, under the glass shade, and 

 carefully secured air-tight, and from injury to itself, by cork 

 and wadding. The plants for comparison were as nearly 

 alike as possible in every respect, and a control phrnt 

 grew in the open air between the shades. Both etiolated 

 seedlings, which became green as quickly without carbon- 



