i] INTRODUCTION 9 



lines of metabolic syntheses in different parts of plants are regulated 

 and correlated with each othe.r. Some of the phenomena involved are 

 shortly outlined as follows. There is undoubtedly, under suitable 

 conditions, a constant synthesis of sugars in the leave's. In all pro- 

 bability aromatic substances are also synthesized in the same organs, 

 for there is evidence that there is an increase of these compounds in the 

 leaf if translocation through the petiole is prevented. It is possible that 

 ^amino-acids also are formed in the leaf. The above products are 

 constantly translocated to the growing organs as material for growth. 

 They may, nevertheless, be temporarily stored in the tissues where they 

 have been synthesized, and of this there is evidence in at least one case, 

 e.g. starch in the leaf. But, apart from the immediate use for growth, 

 there is in practically every plant, some tissue where, owing to some 

 unknown stimulus (causing probably changes in permeability of the 

 cell-membranes), accumulation of compounds occurs. This accumulation 

 is characteristic of organs from which growth will take place when it is 

 impossible for the plant to obtain fresh supplies by carbon assimilation, 

 as, for example, of bulbs, rhizomes, tubers, buds, seeds, fruits and woody 

 tissues. In these cases, in due time, the products stored supply the 

 growing shoots. 



During storage, simple sugars, amino-acids, etc. have been condensed 

 to form insoluble, colloidal, or large molecules of starch, fats, aleurone, 

 cane-sugar, etc. These will remain until they are hydrolyzed by enzymes 

 when they can supply the growing shoots. Such stores are termed 

 "reserve materials." The actual stimuli involved in bringing about and 

 regulating this storage are unknown, but they are probably connected 

 with the life cycle of the particular plant under consideration and its 

 adaptation to external conditions. 



REFERENCES 



1. Abderhalden, B. Biochemisches Handlexikon. Berlin, 1911. 



2. Allen's Commercial Organic Analysis. London, 1909-1917. 



3. Cole, S. W. Practical Physiological Chemistry. Cambridge, 1919. 5th ed. 



4. Czapek, P. Biochemie der Pflanzen. Jena, 1905. 



5. Haas, P., and Hill, T. G. The Chemistry of Plant Products. London, 

 1917. 2nd ed. 



6. Palladin, V. I. Plant Physiology. Edited by B. E. Livingston. Philadelphia, 

 1918. 



7. Plimmer, R. H. A. Practical Organic and Biochemistry. London, 1918. 

 3rd ed. 



