MISCELLANEOl S 189 



I therefore beg leave to point out a few errors ami omissions in the scientific 

 part of the first volume, which may be of minor importance for the practical 

 forester, but would certainly lead to a serious misconception of the physio- 

 logical facts on which all culture of plants is based : — 



In Part II., Chapter 1, under "Atmospheric Air," the author having stated 

 the proportion of nitrogen and oxygen, writes : — " No chemical process is required 

 to separate one constituent from another ; as a matter of fact, all porous bodies 

 possess the faculty of taking oxygen from the atmosphere, without entering into 

 a chemical combination with it. Amongst such bodies are the soil and the leaves 

 of plants. Whether nitrogen is similarly taken up has not yet been proved, but 

 further investigation may lead to important discoveries in this respect, as it is un- 

 likely that the large store of nitrogen should only serve as a dilution of the oxygen. 



This statement is entirely erroneous : as a matter of fact the two gases, though 

 only forming a mechanical mixture, cannot be entirely separated, except by a 

 chemical process, and only to a very small extent by mechanical means as by 

 dilution in water, which is capable of dissolving proportionately more oxygen than 

 nitrogen, or by allowing air to pass through an india-rubber membrane, in which 

 case oxygen passes quicker than nitrogen, owing to the condensing power of 

 india-rubber, which is greater in relation to oxygen than to nitrogen. Porous 

 bodies take up the nitrogen as well as the oxygen, and except where a chemical 

 process or combustion takes place and the oxygen combines with other substances, 

 as in the case of leaves, and frequently in soil, it is only exceptional if ever oxygen 

 is mechanically absorbed in greater proportion than nitrogen. The author proceeds 

 to say : " Although the leaves of plants take up oxygen during the night and in 

 the shade, they exhale greater quantities of it under the effect of light," &c This is 

 but partly correct, as the plants constantly, even in the fullest light, inhale oxygen, 

 exhale carbon dioxide, and breathe just like animals, but this vital action, essen- 

 tial for the preservation of life, is, during the day, through the influence of light, 

 partly obscured by the powerful decomposition of carbon dioxide, by which 

 process carbon is assimilated and oxygen returned to the air. (Though the plants 

 may at times show no outward sign of absorbing oxygen, there is now no longer 

 any doubt that a sufficient amount of free oxygen is always available for combustion 

 between the molecules of the cells, which enables the plants to live a certain time 

 without the access of oxygen, just as it has been proved to be the case with frogs, &c.) 



Under the heading " Carbon Dioxide," the author states : — " Plants take the 

 great bulk of the carbon dioxide, which they require, through their leaves, from 

 the atmosphere, only a comparatively small portion is taken up through the roots." 

 The fact is that as just stated the green plants only absorb carbon from the car- 

 bon dioxide and return the oxygen. The oxygen necessary for forming car- 

 bonates is taken partly as oxygen from the air, and partly from water and mineral 

 salt. A certain amount of carbon dioxide is taken up by the roots in water and 

 carbonates, but is not assimilated. Parasities and fungi only take up previously 

 assimilated carbon from their food-plants or from decaying organic matter. 



