704 BIOLOGICAL EFFECTS OF RADIATION 



Nightingale (51) found that in the short-day plants, salvia and soy- 

 beans, as well as in buckwheat, an indeterminate type, and the long-day 

 plant, radish, assimilation of nitrate was restricted by a 7-hr. day, whereas 

 a 6-hr. day did not greatly limit nitrogen assimilation in the indeterminate 

 plant, tomato, provided available carbohydrate was present. In a 

 14-hr. day tomato made little growth and was unfruitful if the nitrogen 

 supply was deficient, but it was vigorously vegetative and fruitful when 

 nitrogen was freely supplied. When the same plants were transferred to 

 a 6-hr. day, they elongated rapidly and flowered freely if nitrogen was 

 still deficient, and associated with the increased growth the percentage 

 content of carbohydrates decreased and that of nitrogen increased. If 

 nitrogen was amply supplied both before and after the transfer, growth 

 and flowering were checked, and associated with the decreased growth 

 the percentage content of carbohydrates decreased and that of nitrogen 

 increased. In a 6-hr. day the tomato plants were moderately vegetative 

 and flowered freely when nitrogen was deficient but were weakly vegeta- 

 tive and unfruitful with nitrogen freely supplied. Transfer from the 

 6-hr. to the 14-hr. day, with deficient and with ample supplies of nitrogen, 

 reversed the effects on growth and reproduction of the transfers from 

 long to short day, and the associated changes in relative contents of 

 carbohydrates and nitrogen also were reversed. In salvia exposed to a 

 short day there was accumulation of carbohydrate, presumably because 

 there was little utilization of it in synthetic processes. Transfer of 

 high-carbohydrate salvia plants from a short to a long day resulted in 

 rapid growth in association with loss of carbohydrates and increased 

 assimilation of nitrates. The root system of weakly vegetative high- 

 carbohydrate plants was relatively much more extensive than that 

 of vigorously vegetative low-carbohydrate plants. 



On the basis of observations made on Phaseolus multijiorus and data 

 reported by others Tincker (72) concludes that there is a correlation 

 between the C/N ratio and the behavior of the plant, though it does 

 not follow that the magnitude of the ratio actually determines plant 

 behavior, for the reverse may be true. It appears that length of day 

 influences the rate of elongation of the stem and controls utilization of 

 photosynthetic compounds, in this way influencing the C/N ratio of the 

 tissues. In contrast with the conclusions of previous workers, Arthur 

 and others (5), as a result of extensive observations on many species 

 grown under accurately controlled conditions and exposed to various 

 day lengths, were unable to find any relation between carbohydrate and 

 nitrogen content and flowering in either long-day plants, such as radish 

 and lettuce, or in the short-day plant, salvia, or in buckwheat, an indeter- 

 minate type. It was found that percentage content of carbohydrate 

 and nitrogen in general can be changed by varying light intensity, 

 length of day, and in some cases by changing the nitrogen supply. 



