354 PHYSIOLOGY OF NUTRITION. 



the cause of this is to be sought in the anatomical structure of 

 the stem. In Salix soft bast elements occur only at the periphery 

 of the vascular bundles. Nerium possesses soft bast not only on 

 the outside, but also on the inside of the vascular bundles, as 

 is easily made out microscopically by examining delicate trans- 

 verse sections. In Nerium, therefore, the path for the conduction 

 of proteids is by no means completely blocked by ringing, while 

 .in Salix it is. In Nerium considerable quantities of non-nitro- 

 genous and also nitrogenous plastic material can stream to the 

 parts of the stem lying below the ring, and for this reason a fairly 

 large formation of roots is possible in this lower portion of the 

 stem. 1 * 



As regards the migration of non-nitrogenous bodies in trees and 

 shrubs under normal conditions of environment, there is no 

 doubt, according to the investigations of Th. Hartig, Sachs, and 

 A. Fischer, 2 that the carbohydrates formed in the leaves are trans- 

 located almost exclusively in the parenchyma of the cortex, while 

 the upward movement of the carbohydrates in the spring, when 

 the buds are bursting, takes place in the glucose-containing 

 vessels of the wood. 



A several-years-old branch of Betula, the lower end of which 

 must be without branches and leaves, is ringed at the beginning 

 of June about 10 cm. above its point of insertion, without being 

 removed from the parent plant. The exposed wood is smeared 

 with grafting wax. At the commencement of August we cut the 

 branch and test suitable transverse sections for starch. It is 

 often sufficient to examine macroscopically, by moistening trans- 

 verse slices with Iodine solution. Above the ring the wood and 

 oortex prove to be extremely rich in starch. The wood at the ring 

 is very poor in starch ; so also are the wood and cortex below the 

 ring. The carbohydrates clearly could not pass the ring, because 

 here there was no cortex. In the uninjured branch, on the 

 contrary, they move downwards in the cortical parenchyma, and 

 thence distribute themselves to the wood, the medullary rays, 

 and the pith, where they are deposited in the form of starch. 



The fact that the carbohydrates move upwards in the wood 

 at the time of the bursting of the buds is determined by the 



* Proteids can, however, in many cases be translocated also in the wood. 

 See Strasburger, Ban und Verrichtung der Leitungsbahnen, 1891, pp. 900 and 

 901. The translocation of amides, etc., takes place in the parenchyma. 



