INDIVIDUAL ELEMENTS 



139 



— substances always present in the cell nucleus — in lecithins, in hexose 

 phosphoric acid which is essential to zymase activity in yeast and prob- 

 ably to the activity of similar enzymes in all plant tissues. The globoid 

 in aleurone grains is composed of calcium-magnesium phosphate. / 



Translocation and Use of Phosphorus-containing Compounds. — The 

 distribution of phosphorus in the fruit tree is very similar to that of 

 nitrogen. Young tissue is richer in phosphorus than older tissue, young 

 leaves and young bark being particularly rich in this element and much 

 the same relations hold in regard to elaboration, storage and utilization 

 of phosphorus as with nitrogen. Most tissues contain approximately 

 six times as much nitrogen as phosphorus. This holds roughly for 

 trunk and branches, new growth, buds and young leaves. The older 

 leaves have less phosphorus, the fruit and the apple spur more. The 

 general constancy of the phosphorus-nitrogen ratio indicates that the 

 two elements may be combined in the same molecule. Nucleins, nucleo- 

 proteins and lecithin contain both elements and are of universal occur- 

 rence in all living plant tissues. Table 24 shows the relative amounts of 

 the various types of organic phosphorus in developing grape seeds. The 

 bulk is nuclein phosphorus and should this be the case in most plant 

 tissues the relative constancy of the nitrogen-phosphorus ratio would 

 be explained. 



Table 24. 



-The Phosphorus Content of Grape Seeds'' 

 (In percentages of fresh weight) 



Hard, Sept. 6 



Softening, Sept. 

 30 



Ripe, Oct. 30 



Lecithin P. . . . 

 Nuclein P. . . . 

 HCl-soluble P 



0.0017 

 0.0159 

 0.0019 



o.oinr, 



o.oois 



0.0184 

 0.0016 



0.0218 



0.0021 

 0.0197 

 0.0016 



0.0234 



Nevertheless distinct differences exist between the variations in the 

 nitrogen and in the phosphorus content of the same tissue and these 

 show that phosphorus compounds do not play the same part in plant 

 metabolism as nitrogen compounds. 



If organic phosphorus-containing compounds are built up chiefly in 

 the leaves, they pass out of the leaves as fast as they are made and are 

 used by the developing fruit and in the growth of vegetative tissues. 

 Before the leaves fall, a considerable amount of their phosphorus is 

 withdrawn and stored in the phloem. The phosphorus used in the first 

 stages of growth in the spring and in the initiation of fruit development is 

 obtained from stored compounds. 



