518 Theory of the Nutrition [BOOK in. 



is decomposed in the day-time; the carbon is fixed in the plant 

 and the oxygen discharged as gas into the air. The immediate 

 result of this operation appears to be the formation of a sub- 

 stance which in its simplest and most ordinary state is a kind of 

 gum consisting of one atom of water and one of carbon, and 

 which may be changed with very little alteration into starch, 

 sugar, and lignine, the composition of which is almost the same. 

 The nutrient sap thus produced descends during the night from 

 the leaves to the roots, by way of the rind and the alburnum in 

 Exogens, by way of the wood in Endogens. On its way it falls 

 in with glands or glandular cells, especially in the rind and 

 near the place where it was first formed ; these fill themselves 

 with the sap and generate special substances in their interior, 

 most of which are of no use in the nutrition of the plant, but 

 are destined either to be discharged into the outer air or to be 

 conducted to other parts of the tissue. The sap deposits in its 

 course the food-material, which becoming more or less mixed 

 up with the ascending crude sap in the wood, or sucked in with 

 the water which the parenchyma of the rind draws to itself 

 through the medullary rays, is absorbed by the cells and chiefly 

 by the roundish or only slightly elongated cells, and is there 

 further elaborated. This storing up of food-material, which 

 consists chiefly of gum, starch, sugar, perhaps also lignine, and 

 sometimes fatty oil, takes place copiously in organs appointed 

 for the purpose, from which this material is again removed to 

 serve for the nourishment of other organs. The water, which 

 rises from the roots to the leaf-like parts of the plant, reaches 

 them in an almost pure state, if it passes quickly through the 

 woody parts, the molecules of which are but slightly soluble. 

 If, on the other hand, the water flows through parts in which 

 there is much roundish cell-tissue filled with food-material, it 

 moves more slowly and mixes with this material and dissolves 

 it; when it is drawn away from these places by the vital activity 

 of the growing parts, it reaches them not as pure water but 

 charged with nutrient substances. The juices of plants appear 



