CHAP, iv.] The Food of Trees 71 



tained in the parenchym of the leaves, and is assimilated, or 

 prepared for being made of use for structural purposes, in 

 different combinations of carbon l . As on the average 0-03 % 

 by volume, and 0^05 % by weight, of the atmosphere consists of 

 carbonic acid, there is never any want of this essential factor 

 to the due thriving of any kind of woodland tree in any 

 given locality. 



Whilst there is no reason to deny to ordinary plants, with 

 foliage containing chlorophyll, a certain capacity for absorbing 

 nutriment directly from humus or organic matter in the soil, as 

 is done by those which are not provided with chlorophyll, yet 

 the thriving of woodland growth on soils poor in humus is of 

 itself a proof that any direct absorption of carbon compounds 

 by the root-system cannot be of essential importance to their 

 existence. The discovery, by Sadebeck and Frank about nine 

 or ten years ago, of the mantle of fungoid tissue around the 

 extreme points of the rootlets of cupuliferous trees (Oak, Beech, 

 and Chestnut), and since also proved in the case of other 

 woodland trees, coniferous as well as deciduous, has given rise 

 to a theory that the introduction of organic matter is often 

 carried on by means of the symbiosis of a fungus or Mycorhiza at 

 the points of the suction-roots. This Mycorhiza is supposed by 

 Frank to act as a go-between, absorbing water, and nitrogenous 

 and non-nitrogenous organic matter from the soil, and giving 

 these to the rootlets, from which again the fungus receives other 

 nourishment in exchange. According to Ramann 2 , however, 

 the appearance of the Mycorhiza must be considered as already 

 the indication of an abnormal or diseased condition, rather than 



1 The chemical process is probably as follows (see R. Hartig's Anatomie 

 und Physiologic der Pflanzen, 1891, pp. 172 and 229): C 2 O + H 2 O = 

 CH 2 O -f 2O set free ; 6(CH a O) = C 6 H 12 O<, dextrin, glucose, or grape 

 sugar, in which form the assimilated product is capable of being translated 

 from the leaves to other parts of the organism. When formed quicker 

 than it can be transported, this loses one molecule of H 2 O, and becomes 

 C 6 H IO O 5 or starch, which is secreted temporarily in the solid form and 

 transformed again into grape sugar, when required, by resuming the molecule 

 of H 2 O. 



3 Ramann, Forstliche Bodenkunde und Standortslehre, 1893, p. 302. 



