100 HISTORY OF BOTANY 



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 substance 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 httle alteration into starch, sugar, 

 and hgnine, 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 alburnimi 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 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 shghtly 

 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 



