CARBOHYDRATES AND NITROGEN METABOLISM 451 



Each of these conditions was distinguished by characteristic morphological 

 responses on the part of the plants: 



I. Very low proportion of available carbohydrates to available nitrogen. 

 Plants were weakly vegetative and unfruitful. The few flowers which 

 formed abscised. Stems were slender, succulent and a light grayish-green in 

 color. Chemical analysis showed that the plants contained practically no 

 reserve carbohydrates, but a relatively large quantity of available nitrogenous 

 compounds. 



II. Low proportion of available carbohydrates to available nitrogen. 

 Plants were vigorously vegetative but unfruitful. Stems were thick, pithy, 

 and succulent. Leaves were large, soft, and dark green. Chemical analysis 

 showed the plants to be low in reserve carbohydrates, but relatively high in 

 available nitrogenous compounds. 



III. Intermediate proportion of available carbohydrates to available nitro- 

 gen. These plants had proportionately more carbohydrates than those in 

 class II but nevertheless were not deficient in nitrogen. They exhibited good 

 vegetative growth and good reproductive development. Stems were thick 

 and relatively woody. Leaves were well developed and a normal green in 

 color. Chemical analysis showed these plants to contain considerable reserve 

 carbohydrate and to be lower in available nitrogenous compounds than those 

 of class II. 



IV. High proportion of available carbohydrates to available nitrogen. 

 Plants were feebly vegetative and unfruitful. Most flowers abscised, although 

 a few small, woody fruits were set. Stems were slender, hard, and woody. 

 Leaves were small, stiff, and light green to yellow in color. Chemical 

 analysis showed the plants to contain relatively large quantities of stored 

 carbohydrates, but very little available nitrogen in any form. 



Any interpretation of the results of Kraus and Kraybill and the similar 

 results of a number of other investigators must be based on an evaluation of 

 the relative roles of carbohydrate and nitrogenous foods at different stages m 

 the growth cj-cle of a plant. The best "carbohydrate-nitrogen ratio" for one 

 stage in the development of a plant is not necessarily the best for other stages. 

 For example, in the wheat plant the proportion of available carbohydrates to 

 available nitrogenous compounds increases progressively throughout the vege- 

 tative period, and flowering occurs when this proportion becomes sufliciently 

 high (Hicks, 1928). 



The effects of carbohydrate and nitrogen metabolism on vegetative de- 

 velopment will first be considered. Next to water proteins are the chief 

 constituent of the protoplasm of active cells, while the cell walls are con- 

 structed almost entirely of carbohydrates. Continued development of new 



