Chemical Factors in General 367 



The relation of the C/N ratio to flowering is evident in many ways. In 

 biennially bearing apple trees, for example, it is high in the bearing 

 years and low in the "off" ones. In fruit spurs where the buds are de- 

 veloping into flower buds, starch content tends to be high and nitrogen 

 low, whereas in barren spurs the opposite is true. Potter and Phillips 

 (1927), however, found that flower-bud formation in fruit spurs was 

 more closely related to the amount of nitrogen than to any ratio be- 

 tween this element and carbohydrates. 



Loomis ( 1932 ) has emphasized the fact that the effect of water on 

 development resembles that of nitrogen, both tending to stimulate vege- 

 tative growth. He believes that the balance is not so much between carbo- 

 hydrate and nitrogen as between the factors that tend to produce growth 

 and those that tend to induce differentiation. The former include both 

 water and nitrogen together with any other factors, such as temperature, 

 that favor the synthesis of new protoplasm. Differentiation, on the other 

 hand, requires an excess of available carbohydrate. Why this is so is by 

 no means clear, though there may be a selective advantage in a mecha- 

 nism which tends to defer the development of reproductive structures 

 until a plant has reached the size where it is large enough to produce 

 fruit abundantly. 



The carbohydrate-nitrogen ratio is related to other structures than 

 reproductive ones, notably the shoot-root ratio. In general, the higher the 

 C/N ratio, the larger is the relative size of the root. When nitrogen is 

 abundantly available in the soil, the increased growth tends to occur 

 in the shoot more than in the root. Hicks ( 1928b ) found that in willow 

 cuttings the carbohydrates pass downward and the nitrogen upward so 

 that the C/N ratio is higher at the base, where roots develop, than at 

 the tip, where shoots are formed. Da vies (1931) also observed that in 

 willow cuttings roots develop in regions where nitrogen, as a percentage 

 of dry weight, is low and shoots where it is high. These facts obviously 

 have a bearing on the problem of polarity in regeneration (p. 119). 



Reid (1924) made stem cuttings from tomato plants that were high in 

 C/N ratio and from others that were low and found that the former made 

 better roots than the latter. She also observed (1929) that the relative 

 development of the root in seedlings of various species was related to 

 the proportion of carbohydrate to nitrogen in the seed from which 

 they grew. Where this was high the seedlings had stronger roots than 

 where it was low. 



Despite the evident relation between the C/N ratio, as observable in 

 the chemical composition of the plant, and the processes of flowering and 

 root formation, there is now a good deal of evidence that this ratio may 

 not be the cause but rather an accompaniment of these activities. In a 

 number of instances, such as the soybean (Murneek, 1937) and wheat 



