CHAP, vi The Metabolic Processes 373 



manner and path of their transport. The problem included, 

 however, something more than this, viz. the relations 

 between the first-formed substances and the actual con- 

 stituents of the elaborated sap or formative mucilage of 

 Hartig. 



We have already traced the course of investigation into 

 the first of these questions as far as the end of the century. 

 It remains for us to deal with the general inquiry into 

 the phenomena which follow the construction of what we 

 are now able to recognize as the actual food of the vegetable 

 organism, which was known to be transported in some form 

 from the leaves. 



In this field Sachs was again a pioneer. He was the 

 first to subject the old theory of the circulation of the 

 sap to a close scrutiny, gaining extensive knowledge as to 

 the way in which translocation of the different foodstuffs 

 takes place, the exact nature of many of the products 

 concerned, and the means by which such translocation is 

 secured. He ascertained further that such processes of 

 removal or transport are often associated with decomposi- 

 tions and recombinations in the channels through which 

 they pass. 



The somewhat vague ideas as to the descending sap 

 were given a little more definiteness in 1860 through some 

 observations of Hanstein. \Yhen he removed from a young 

 sapling a ring of cortical tissue extending from the exterior 

 to the cambium, thus cutting away entirely the cortex and 

 the phloem of the vascular bundles, he found the operation 

 was followed by a formation of adventitious roots above 

 the injury, but not below it, indicating that whatever the 

 descending sap may be, it contains formative material, 

 and that it travels in either the bast or the cortex of 

 a young tree. Hanstein's work was repeated in 1879 by 

 Faivre, and his results confirmed. These observations, 

 however, gave no information on either of the problems 



