214 PLANT PHYSIOLOGY 



102 cwt. of dry substance per hectare. In best years, the yield 

 may increase up to 60 cwt. of grain and 80 cwt. of straw, i.e., 

 119 cwt. of dry substance per hectare. 



For sugar beets the average yield attains 400 cwt. of roots 

 and 400 cwt. of leaves. Calculating from these figures the dry 

 weight, we obtain correspondingly 96 and 64 cwt., i.e., a sum of 

 160 cwt. per hectare. In the most favorable years, the yield 

 of roots increases to 700 cwt., and the total dry substance 

 reaches 280 cwt. The greater productivity of sugar beets 

 depends first of all on their considerably longer vegetative period 

 as compared with that of wheat. Besides, during the first 

 year, sugar beets produce only vegetative organs and thus do 

 not expend organic substance for flowering and maturing of 

 fruit. 



It is very probable that the maximum yields stated by Bondorff 

 do not yet represent the limits of productivity and that with a 

 more careful study of the requirements of plants and with further 

 improvement of the methods of tillage, irrigation, and fertilizing 

 crop plants, it may be possible to obtain jdelds exceeding by far 

 those mentioned by Bondorff. 



49. General Course of the Accumulation of Organic Substance 

 by the Plant during Its Vegetation. — If the progress of the 

 accumulation of organic substance of some annual plant is fol- 

 lowed from day to day, from germination up to maturity, a 

 definite regularity may be observed. The daily increase is very 

 insignificant in the beginning but rapidly augments and reaches 

 its maximum usually before flowering. After flowering, it 

 gradually decreases and finally ceases entirely. Very often, 

 after this, there occurs a certain loss in organic substance. 



It is not possible to determine the increase in dry matter in 

 the course of the development of the plant from one and the same 

 specimen throughout, as it must be weighed dry; otherwise the 

 changes in its amount will be masked by variations in water 

 content. For this purpose, the plants must be grown in a field 

 plot as uniform as possible, and not less than 50 or 100 specimens 

 must be picked for every determination, in order to average the 

 inevitable individual variations. 



In the following table is presented an example of the progress 

 of accumulation of dry substance by corn, studied in detail by 

 Miller in Kansas in 1925. 



