342 



BOTANICAL GAZETTE [November 



photosynthetic activity to balance the nitrates absorbed, or to 

 the higher carbohydrate-nitrogen ratio accompanying best grain 

 production. Which of these three possibilities really determines 

 the situation can only be answered by such studies as those 

 made or suggested on the tomato by Kraus and Kraybill, or 

 studies of the type made in this paper. It is evident, however, 

 that there is need of numerous studies of the carbohydrate- 

 nitrogen ratio in plants, both in regard to the factors affecting this 

 ratio and the effect of the ratio on plant characters. As was sug- 

 gested in the review of the hterature at the beginning of this article, 

 such studies are likely to throw much light on other physiological 

 features than vegetation and reproduction. 



Summary 



1 . There is a large amount of nitrate in the organs of A . retro- 

 flexus. The stem and branches are the primary nitrate storage 

 organs. The rate of nitrate absorption increases with the aging 

 of the plant, perhaps partly being due to the development of the 

 root system with numerous branching rootlets, increasing the radius 

 of the feeding area from a few inches to 2 ft. or more. 



2. This high capacity for nitrate absorption and storage must 

 be an important factor in making Amaranthus a very successful 

 competitor against cultivated plants, so effectively withdrawing 

 as it does the nutrient element most commonly limiting plant pro- 

 duction. It would be interesting to know how generally and to 

 what degree weeds possess this power. 



3. The carbohydrates and nitrogen compounds fluctuate 

 throughout the growing period. The fluctuation of the carbo- 

 hydrates is in the reverse order of the nitrogen compounds. This 

 inverse ratio is not a truly mathematical constant, but in general 

 when the carbohydrates are high the nitrogen compounds are low, 

 and vice versa. As the nitrate nitrogen composes more than 50 

 per cent in the stems and branches, there is a possibility that 

 nitrates have some modifying effects on this reciprocal relationship. 

 This inverse ratio is due partly to the synthesis of protein, chloro- 

 phyll, phospholipin, and other organic nitrogen compounds at the 

 expense of the soluble carbohydrates. 



