214 HISTORY OF BOTANY 



term " food-stuffs " might be legitimately applied ; the 

 second, the appropriation of these food-stuffs by the 

 protoplasm, with the accompanying phenomena known 

 to the animal physiologist as digestion and assimilation. 



There has been much controversy over the terminology 

 of these anabolic phases, but I need not trouble you with 

 the arguments for and against the use of such words as 

 " photosyntax," " photosynthesis," " carbon assimila- 

 tion," and so on ; the important thing is to recognise 

 that these phases in plant nutrition exist, and, as I have 

 already frequently pointed out to you, that the animal 

 differs from the plant in starting its nutritive processes, 

 so to speak, at a higher level than does the plant. 



As to the details of the metabolic changes, between 

 the primary acquisition of the raw materials and the 

 development of the finished product, Uttle was known 

 up to the middle of the nineteenth century. Indeed as 

 late as i860 the general account given in the textbooks 

 was that " crude sap," as it was called, ascended by way 

 of the xylem of the root and stem, became " elaborated " 

 in some mysterious way in the leaf when that organ was 

 exposed to light and air, and that the " elaborated sap " 

 then descended in the form of a kind of mucilage or gum, 

 from which reserve materials were condensed and deposited 

 in various situations. 



The first step in the enquiry into metaboHsm in general 

 was taken by Hanstein, who, in i860, showed that the 

 removal of all tissues external to the cambium was 

 followed by the development of adventitious roots 

 above the wound. The obvious deduction was that the 

 descending " elaborated sap " provided materials required 

 for the growth of these roots, i.e. manufactured plasta. 

 Sachs in 1864, and Godlewski and Pfeffer in 1873, showed 

 quite conclusively that the starch that accumulated in 

 the leaf as a result of photosynthetic activity in light 

 was removed in whole or in part not only during the night 

 but also by day in the form of a sugar. The method of 



