350 Mineral Nutrition of Plants 



piration. Thus, in the vegetative phases, carbohydrate supply is the con- 

 trolling factor in protein synthesis, while oxygen supply becomes a 

 major regulatory factor in the synthesis of proteins during the repro- 

 ductive phase. 



In addition to the foregoing functional factors influencing the water 

 economy of the flowering shoot, vascular tissues also undergo compli- 

 cating structural modifications (30, 31, 74, 113, 125, 130, 131, 143, 149). 

 The work of several investigators (116, ijq) reveals a subsidence in 

 cambial activity which begins in the vicinity of floral buds and com- 

 monly extends progressively toward the base of the stem (125). Phloem 

 formation especially seems to be reduced and failure of vascular differ- 

 entiation commonly involves pedicels or fruits stalks, thus often im- 

 pairing fruit setting or fruit enlargement (27). The impairment of con- 

 duction appears during the flowering stage and retards the redistribu- 

 tion of nutrients; the reduction in conductive capacity of vascular bun- 

 dles in stems and pedicels may become a temporarily limiting factor 

 in the rate of growth of the shoot apex and of fruits. 



THE FRUITING STAGE 



The fruiting stage has its origin in syngamy. The early stages of fruit 

 enlargement are commonly associated with marked increments in ab- 

 sorption by roots and accelerated anabolism of the younger parts of the 

 shoot (13, 18, 27, 34, 42, 6$, 74, gi, 94, 100, 127, 144, 145, 150). Gains in 

 nitrogen and potassium become appreciably higher (74). Absorption of 

 phosphorus and iron, though fairly steady at first, tend to rise, some- 

 times to surprisingly high levels as maturation supervenes (44, 1 17, 139). 

 There is an increased accumulation of proteins and carbohydrates, the 

 latter usually being the greater in terms of dry weight gains (127). 

 The origin of the systemic stimulus to accelerated activity following 

 syngamy appears to be associated with increments in growth substances 

 at reproductive loci and their translocation to adjacent tissues (8, 88). 



As would be expected, increasing amounts of organic and inorganic 

 reserves are diverted from vegetative to reproductive organs as more 

 fruits are set and their enlargement accelerates (28, 73, go, 145). It is 

 interesting to observe, however, the comparatively uniform composi- 

 tion of seeds and fruits in relation to the frequently great differences in 



