352 Mineral Nutrition of Plants 



nitrogen and aeration of the substrate (146). The effects of elements 

 other than nitrogen also appear to vary significantly with the stage of 

 development at which applied (101, 105, 144). 



The phenomena of nutrient balance between vegetative organs and 

 fruits, especially in heavily fruiting varieties such as cotton and tomato, 

 have been described by many investigators. The effects of a heavy crop 

 of fruit in depleting the nitrogen reserves of leaves and stems are 

 rather well known, as also are the cyclic renewals of vegetative activity 

 when fruit abscission or maturation occurs (28, 73, go, 137, 145). The 

 usual course of events in numerous annuals is the depletion of leaves 

 to the point of protoplasmic disintegration and the rapid initiation of 

 senescence terminating in abscission or death of leaves and excretion 

 of mineral elements by roots to substrate (35, 36, 37, 44, 61, 69). 



In conclusion it may be noted that, though mineral nutrients are not 

 the initial and primary causes of tissue differentiation or inception of 

 reproductive processes, they are often controlling factors in the imple- 

 mentation of the plants' developmental potentialities. Recent work dis- 

 closes the intimate relation of mineral elements to the formative action 

 of growth substances (66), to the respiratory action of nucleotides, and 

 to other intermediates in oxidative metabolism. Thus, the action of 

 phytohormones and other specifically morphogenetic compounds is in- 

 timately correlated with mineral nutrients much as the inorganic ions 

 are related to photosynthesis, enzyme action, and other vital functions 

 in the regulation of growth and the ontogenetic cycle. 



REFERENCES 



1. Achromeiko, A. I., Jahrb. Pflanzenernlihr-Diing. und Boden\unde, 

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2. Ali-Zade, M., Doklady A\ad. Nau\ S.S.S.R., 30:254 (1941); Chem. 

 Abstracts, 35:8016 (1941). 



3. Anderson, P. J., Swanback, T. R., and Street, O. E., Conn. Agr. 

 Expt. Sta. Bull., 422:6 (1939). 



4. Andre, G., Compt. rend., 154:1817 (1912); 151:1378 (1910); 156:1164 

 (1913); 152:965 (1911). 



5. Arnon, D. I., and Hoacland, D. R., Botan. Gaz., 104:576 (1943). 



6. Avdonin, N. S., Soc. zern. Hoz., 4:127 (1939); Herb. Abstracts, 10: 

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