208 GROWTH 



moderate vegetative growth and good reproduction ; and when 

 the C/N ratio is very low, a vigorous vegetative growth and 

 poor reproduction obtains. Thus the best results occur when 

 these two factors arc reasonably balanced. 



This important work, which is well substantiated, stimu- 

 lated investigation on this aspect of nutrition in relation to 

 growth, and many papers have been published on this and 

 cognate subjects. A summary of these will be found in the 

 memoirs of Hicks and of Tincker. The former * is concerned 

 with the carbon/nitrogen ratio in the wheat plant in which is 

 traced the change in the ratio from the seedling to the grain. 

 A large number of analyses show that the early stages of ger- 

 mination are characterized by a low C/N ratio which steadily 

 rises throughout the vegetative period ; when sufficiently 

 high, flowering occurs. Fruit development is characterized 

 by a low C/N, the amount of nitrogen being high. Active 

 meristematic tissues have a low ratio, which increases with 

 age ; and senescent tissues have a high C/N ratio. For these 

 reasons the conclusion is reached that the younger the tissue 

 the lower is the C/N ratio. From a consideration of the avail- 

 able evidence, Tincker f concludes that flower production is 

 initiated by the metabolic balance in which the carbohydrate/ 

 protein ratio lies within certain limits ; the dislocation of this 

 ratio, either by the excess or the deficiency of one component, 

 retards flower production. Clearly the problem is involved 

 with photo-periodicity, the period of illumination operating by 

 altering the carbohydrate factor and, by its transpiration effect, 

 the nitrogen content. Thus short-day plants subjected to a 

 lessened period of illumination show a greater carbohydrate 

 content, a lesser elongation of the axes, and the production 

 of flowers ; but when treated with long days, vegetative 

 growth is promoted and reproduction is eliminated, presum- 

 ably because the C/N ratio is too low for flower produc- 

 tion. For long-day plants, a lessened period of illumination 

 increases the starch content and eliminates flowering, possibly 

 owing to the unsuitability of the available carbohydrate ; 



* Hicks : " New Phyt.," T928, 27, I, 108. 

 I Tincker : " Ann. Bot.,*' 1925, 39, 721. 



