INDIVIDUAL ELEMENTS 131 



synthetic process, predominates in direct sunlight. According to one 

 investigator^^^ the influence of Hght in favoring protein formation and 

 the elaboration of inorganic to organic nitrogenous compounds becomes 

 more pronounced as the stage of development advances. Nitrogen 

 elaboration can take place in the absence of chlorophyll and light, in 

 which case presumably carbohydrates are used.-"^ The amino-acids 

 which are the first products of elaboration are either used directly in 

 the leaf or are conducted through the phloem to all parts of the plant 

 where they are used in the building up of every nitrogen-containing 

 organic compound found in plants as well as of certain nitrogen-free 

 organic substances (essential oils, resins and polyterpenes). The amino- 

 acids are combined to form the proteins which occur in all protoplasm. 

 Other nitrogenous organic compounds are the purines and pyrimidines 

 which enter into the composition of nucleic acids, nucleins and nucleo- 

 proteins, substances characteristic of the cell nucleus. Lecithins and 

 chlorophyll contain nitrogen. Nitrogen-containing compounds which 

 are not of universal occurrence are the alkaloids, ptomaines, amines, 

 cyanogenetic glucosides and indican (natural indigo blue). 



Translocation and Use of Elaborated Nitrogenous Compounds. — The 

 elaboration of nitrates to amino-acids beginning at the time the leaves 

 are well developed, proceeds as long as they remain green, reaching a 

 maximum when temperature, light and soil supply conditions are at an 

 optimum. The elaborated nitrogen-containing compounds are con- 

 stantly passing out of the leaves throughout the season of elaboration as 

 fast as they are made. They are used for new tissue development, for 

 shoot growth, new leaves, increments to branches, trunks and roots, new 

 roots and especially for fruit and seed development. A considerable part 

 of the remainder is stored in the phloem. Storage is particularly rapid 

 in the fall when growth has ceased and before the leaves are separated 

 from the plant by abscission layers. 



New tissue growth in early spring is at the expense of stored foods, 

 including stored nitrogen. This reserve supplies the developing shoots, 

 leaves, flowers, rootlets, much of the new tissue in trunk, branches and 

 roots and the fruit in its initial stages. Hence for good spring growth of 

 tissues, especially shoots, leaves and spurs, abundant nitrogen storage the 

 previous season is a prime requisite. This, in turn, depends on a 

 good supply of available nitrogen in the soil between June 1 and Sept. 15 

 or Oct. 15, a supply more than sufficient for fruit and tissue development. 

 Summer defoliation or a diseased condition of the leaves evidently checks 

 growth the following year by cutting down the supply of stored and elabo- 

 rated nitrogen. 



Attention should be called to the apparent usefulness of unelaborated 

 nitrogen to the apple and pear tree and probably to other fruits, through 

 enabhng them to set a larger crop. It is a common experience to secure 



