220 FORMATION OF PROTEINS 



is therefore a decrease in the dry weight of the plants. However, 

 when the leaves and organs which effect ' carbon-fixation ' have 

 been developed, there is usually a continuous increase in dry 

 weight from the beginning to the end of the life of a plant, 

 anabolism being largely in excess of catabolisni. 



The larger proportion of the sugars, fats, proteins and other 

 organic compounds manufactured by the plant, are employed in 

 the construction of the cell-walls and protoplasm of the new cells 

 arising at the growing points, and in nourishing the protoplasm 

 of more mature cells and also in thickening the walls of the latter. 

 Under ordinary conditions of growth more organic material is 

 constructed than is needed for the immediate nutritive require- 

 ments of the individual plant ; the excess is stored for the 

 nutrition of its oifspring, and, in the case of a perennial, for 

 its own nutrition at subsequent periods of its growth. 



According to Brown and Morris' researches cane-sugar appears 

 to be the first sugar formed in the 'carbon-fixation' process 

 carried on by green leaves. 



The cane-sugar appears to be subsequently transformed by the 

 enzyme invertase in the leaves into dextrose and levulose ; the 

 latter sugars then travel from the leaf-blade through the petiole 

 and into the stem along which they are translocated to the buds, 

 growing-points and other parts of the root and shoot where 

 growth and the formation of new organs or new tissues are 

 taking place, and also to the centres, where storage of reserve- 

 foods is occurring. 



The starch formed in the chloroplasts of the leaf-blade, is 

 acted on by the enzyme diastase present in the cells and 

 becomes transformed into maltose which travels from the leaf 

 with the rest of the sugars to the centres of nutrition and 

 storage. 



Diastase increases in leaves kept in the dark, and in con- 

 sequence the disappearance of starch goes on most rapidly at 

 night 



