46 PROPAGATION OE PLANTS. 



mineral masses of the globe, but it is present in the air 

 in combination with nitrogen. 



Carbon is a constituent of every organic compound, 

 and even the lowest order of plants, that consist only of a 

 single cell, is supposed to have the power of decomposing 

 and utilizing carbonic acid. On an average, forty to 

 fifty per cent, of the weight of plants, v^hcn perfectly 

 dry, is carbon, and in some trees and shrubs the percent- 

 age is still greater, as shown when burned for charcoal. 

 From whence all this carbon is derived is as far from 

 being a settled question among vegetable physiologists as 

 is that of how it finds an entrance to the cells of plants, 

 referred to on a preceding page. Some authors assert 

 that it is all derived from the atmosphere through the 

 leaves, while other^ are just as positive that it is taken 

 up by the roots and then decomposed, combined, or re- 

 organized in the cells. Prof. C. H. Goessmann, in " Man- 

 ual of Agriculture," 1885, says : "that both carbonic acid 

 and ammonia are always found in the atmosphere, and 

 are taken in by the leaves or dissolved by the rain falling 

 through the air and carried into the earth, where they are 

 absorbed by the roots." Prof. Moll, an eminent German 

 authority, so late as 1878, claims that " roots take no 

 part in supplying the plant with carbon dioxide," while 

 Prof. Julius Sachs, in his voluminous work "Text-book 

 of Botany," says "that it is only the cells which contain 

 chlorophyll and these under the influence of sunlight 

 that have the power of decomposing the carbon dioxide 

 taken up by them, and at the same time setting free an 

 equal volume of oxygen in order to produce organic com- 

 pounds out of the elements of carbon dioxide and water, 

 or, in other words, to assimilate." The theories advanced 

 by Prof. Moll and Sachs are also held by many other 

 equally eminent botanists of the present day, while many 

 of our most learned and celebrated chemists, like Prof. 

 Goessmann, dissent, offering equally as good reasons, with 



