BY JAMBS M. PETRIE. 811 



The above experimental evidence would seem to support the 

 suggestion made as early as 1865 by Sachs, that an intimate 

 association exists between the photosynthesis of carbohydrate 

 and the chemosynthesis of protein, and therefore that a large 

 part of the protein may possibly be formed in the carbon- 

 assimilating cells of the green leaf. 



In the metabolism of animals there is a highly important 

 parallelism which Loewi(33) proved in 1902. Proteins were 

 digested with trypsin for a prolonged period, until they no longer 

 gave the biuret reaction. When animals were fed with the 

 cleavage-products as their only nitrogenous food, they lived and 

 thrived; but it was absolutely essential that a plentiful supply of 

 carbohydrates should also be given. His results have since been 

 confirmed by Henriques and Hansen, (34) and Abderhalden,(35) 

 who have also shown that animals can be kept alive even by a 

 part of the hydrolytic products; that portion soluble in alcohol 

 and not precipitated by phosphotungstic acid, namely, the mono- 

 amino-acids, possesses the nutritive value. This close resemblance 

 between animals and plants in the manner of building up their 

 proteins is very significant. 



Nitrogenous Reserve-Materials. 



The intermittent growth of plants necessitates a laying up of 

 reserve-material as stores of food on which they may draw during 

 the periods of rest. A large part of the metabolism is therefore 

 directed towards this end. Such stores are found (a) in the 

 circulating sap in the most plastic form ready for immediate use; 

 (b) in reservoirs such as fleshy roots and stems, medullary rays, 

 cells of vascular tissue, sieve-tubes, laticiferous vessels, etc., stored 

 for short periods; (c) in seeds, bulbs, and tubers as the most per- 

 manent form suitable for periods of absolute rest. These stores 

 of plastic materia] may be divided into nitrogenous and non- 

 nitrogenous substances. The former will be dealt with at some 

 length here; the latter are starch controlled by the diastatic 

 enzymes, hemicelluloses and their enzymes, the c}'tases, and fats 

 controlled by the lipases. 



