TRANSLOCATION AND STORAGE OF FOODS 221 



The sugars and other soluble carbohydrates travel in the 

 plant osmotically from cell to cell, by far the largest amount 

 being transferred from the leaves to the stem through the bast 

 and elongated parenchymatous cells surrounding the vascular 

 bundles ; in the stem and roots these compounds travel through 

 the tissues of the bast and probably to a slight extent through 

 the inner parts of the cortex also. 



The medullary rays receive from the bast the materials 

 manufactured in the leaves, and convey them to the cambium 

 and living portions of the wood needing nourishment. 



Proteins, which diffuse very slowly or not at all through cell- 

 walls, are transferred long distances in stems and roots through 

 the open sieve-tubes of the bast. These compounds are also 

 frequently acted upon by enzymes which decompose them into 

 peptones and the amides, asparagine, leucine and tyrosine, which 

 diffuse with greater ease. 



The stream of sap conveying crude food-materials from the 

 soil to the leaves travels through the wood, but the elaborated 

 foods are translocated chiefly through the bast. 



The removal of a complete ring of ' bark ' from the stem of a 

 tree as far as the wood-tissue does not interfere with the 

 upward flow of water and food-materials, but it prevents the 

 stream of elaborated food from passing down to the roots, and 

 unless the wound is healed by the formation of new conducting- 

 tissue across the exposed part, the roots ultimately die of 

 starvation and the whole tree succumbs. The time during 

 which a tree will live after being ' ringed ' depends upon the 

 kind of tree and also upon the amount of organic material 

 stored in the root-stock and roots before the wound was made. 



' Ringed ' trees may, however, live an indefinite period if 

 adventitious shoots arise below the ' ringed ' part, for these 

 leafy shoots manufacture organic material and as there is an 

 uninterrupted connection between such new shoots and the 

 root-system, the latter can receive a certain amount of nutrient 



