ESSENTIALS OF PLANT 



Grams dry matter 

 produced 

 per pot 



quantities of nitrogen were added to a soil provided with an 

 abundance of all other forms of plant food, all other conditions 

 being favorable. The harvest of the barley gave the following 

 results : 



Grams nitrogen 

 supplied 

 per pot 



O.OOO 0.50 



0.028 2.99 



0.056 5.32 



O.I 12 I0.8o 



o. 168 16.38 



0.224 21.72 



The size of the crop increases with the quantity of nitrogen at 

 the disposal of the plant. The size of the crop thus varies with 

 the quantity of the most deficient form of plant food. The plant 

 food is the controlling condition in these experiments. Plant 

 food, however, is only one requirement of plant life. The 

 amount of the crop is profoundly influenced by rainfall, tempera- 

 ture, and other weather conditions which are embraced under the 

 term season, as well as by the nature of the soil, etc. 



Fig. 4. The growth of oats is proportional to the supply of nitrate 

 of soda, other conditions being favorable (after Wagner). 



The law of minimum holds that the size of the crop is regu- 

 lated by the condition least favorable to the growth of the plant. 



