10 



water as well as the inorganic nutrient salts of the soil, which are 

 chiefly required for the formation in the plant of the organic 

 combinations containing nitrogen, sulphur and phosphorus. In 

 order, however, , to fulfil their chief function, the absorption of water 

 and salts in a profitable and sufficient manner, it is necessary for the 

 root-system to be well developed and healthy. It is likewise 

 necessary that the development of the root-system should keep 

 pa'ce with the growth of the other parts of the tree, so that it can 

 satisfy the constantly increasing demands for the supply of water 

 and nutrient salts made on the roots by the continuous develop- 

 ment of the crown. 



The crown, on the other hand, provides the tree, that is. 

 the whole tree in all its parts, and thus also the roots, with the 

 organic products formed from the organic substances employed 

 in the construction and nutrition of the tree, in that the leaves, with 

 the aid of sun-light, extract carbon from the carbon dioxide of the 

 air an-d convert it into sugar. It is immaterial to us, in what part 

 of the plant the organic combinations containing nitrogen, sulphur 

 and phosphorus, necessary for the construction of all the organs of 

 the tree, are formed from this product of assimilation and the nutri- 

 ent salt? of the soil. We will therefore only mention the fact that a 

 great number of these substances appear to be produced in the 

 leaves, and this during the presence of sunshine. However that 

 may be, it is necessary under all circumstances, that the water and 

 salts from the soil should be transported upwards from the roots, 

 into the other parts of the tree, especially into that part above 

 the soil, which grows most extensively and vigorously, namely 

 the crown ; and that, on the other hand, the products of assimilation,, 

 sugar and other complicated organic substances from the crown,, 

 be conveyed to the other parts of the tree, and down to the 

 vigorously growing roots. 



The sole connecting link between the root-system and the 

 leafy head is the stem. It must therefore contain the means of 

 transport for the organic and inorganic substances. The transport 

 of substances in the stem can take place in sufficient volume only 

 if the channels ,work normally and suffer no interruption. It 

 would, however, be a mistake to assume that the inorganic salts 

 and the water of the soil are transported in the same channels as 

 the organic substances. We are aware that four different principal 

 parts can be distinguished in the stem: the pith, the wood, the 



