W.F.Loehwing 345 



supply is favorable. In early vegetative stages under conditions of bal- 

 anced or constant supply, nitrogen, potassium, and phosphorus com- 

 monly increase faster than calcium, iron, magnesium, and sulfur due 

 in part to the relative immobility of the latter elements within the plant 

 (3, 24, yi, 111 , 112). It may be noted, however, that the rate of absorp- 

 tion of a particular ion is determined not only by its availability in the 

 substrate but also by the concentration thereof already in the plant 

 (20, 47, ji, 136, 75/). Numerous investigations (//, 75) indicate that 

 the beneficial effects of soil fertilization are due primarily to increase 

 in foliar area and of assimilative tissue rather than to increase in effi- 

 ciency of assimilative processes. 



As might be expected in early stages of development when new tis- 

 sues are being formed on a large scale, the young plant is relatively 

 more active in accumulation of water (77, 55, 68, 99, 727, 140), nitrogen, 

 and protein than in its later life (77, 54, 62, y^, 112, 138). On the basis 

 of large amounts of inorganic and amide nitrogen found in young 

 plants under favorable conditions, much of the early intake is in the 

 nature of luxury consumption (47). Experimentally, this is made evi- 

 dent by the fact that gradients of curves for nitrogen accumulation are 

 usually steeper than those for dry weight gains in young plants (77, 6y, 

 j$, 112, 138). Recent work on growth substances and naturally occurr- 

 ing phytohormones indicates important interrelationships of such sub- 

 stances with nitrogen (9, 10), zinc (726, 134), and several other nutrient 

 elements (27, 81). Auxin activity diminishes under conditions of nitro- 

 gen deficiency before lack of nitrogen causes retardation of growth or 

 stem elongation {133)- It has been observed that zinc controls trypto- 

 phane formation and, hence, auxin activity because tryptophane is an 

 auxin precursor. Went (141) discusses the work of Bonner and others 

 on the vitamin requirements of flax, pea, and tomato roots. Flax roots 

 which require pyrimidine and thiazole for growth do not themselves 

 synthesize these thiamin precursors but are normally dependent upon 

 translocation of them from the shoot which can produce them. Root 

 tissue-cultures of flax grow only when pyrimidine and thiazole are 

 added. In this instance, sulfur functions as an organic complex in thia- 

 min. Similar relationships seem to prevail in pea and tomato roots for 

 nicotinic acid and vitamin B 6 , respectively {141). These observations 



