132 



FUNDAMENTALS OF FRUIT PRODUCTION 



a good set of fruit when liberal applications of some readily available 

 nitrogen-carrying fertilizer, such as nitrate of soda, are made to weak 

 trees just before blossoming, though without such applications these 

 same trees would bloom heavily but set little or no fruit. This response 

 by the tree is obtained within 2 or 3 weeks after application of the fer- 

 tilizer and at a season when there is practically no leaf area to build up 

 elaborated foods. It would seem, therefore, that the synthesis of organic 

 nitrogenous compounds can take place in tissues other than the leaves. 



Seasonal Distribution of Nitrogen. — A study of the seasonal variation 

 in nitrogen content of different parts of the plant gives a perspective of 

 the processes of nitrogen elaboration, storage and utilization. 



1/ 



Fig. 11. — Nitrogen content of plum leaves in percentages of dry weight. (Plotted from 

 data given by Richter.*^^) 



In Leaves. — Since the leaf is the principal organ of nitrogen elaboration the 

 seasonal distribution of this element in the leaf is important. Leaf buds have a 

 high percentage of nitrogen; certain analyses show 3.687 per cent, of the dry 

 weight in the cherry and 3.779 per cent, in the plum.i^e Fruit buds have a 

 slightly higher percentage composition in nitrogen, corresponding analyses 

 showing 3.771 per cent, in the cherry and 4.142 per cent, in the plum.i^^ 



Table 16 shows the decrease in percentages of nitrogen in apple, pear and 

 cherry leaves from May to October. ^^^ This is shown even more clearly by the 

 graph in Fig. 11. The accompanying composite table (Table 17) is a good 

 illustration of the steady decrease in the percentage nitrogen content of plum 

 leaves. Though there is a continuous decline in the percentage of nitrogen from 

 May through October, there are two periods of rapid decrease, one in May and 

 the other in September. Between the periods of rapid decrease the percentage 

 composition of the leaf is fairly constant. The first period of decrease is at the 

 time when the leaf is growing rapidly and the available nitrogen supply is limited, 

 because of rapid and simultaneous shoot, wood and root development. The 

 period of relatively constant nitrogen content occurs when nitrogen intake is 



