260 



PLANT PHYSIOLOGY 



the containers are fertilized with one of the elements mentioned. 

 For instance, one series receives only nitrogen; another, potas- 

 sium; and a third, phosphorus. The experiment is continued 

 throughout the vegetative period, and at the end of it the 

 appearance of plants in the different series is compared. 



Fig. 78. — Effects of different fertilizers on wheat in pot cultures. On the 

 extreme left without the fertilization; one next to it fertilized with nitrates; the 

 third with potassium and phosphorus salts. The pot on the extreme right has 

 "eceived complete fertilization {after Wagner). 



If the addition of one of the fertilizers, for instance, nitrogen, 

 increases the yield close to its maximum, this shows that the 

 soil is especially in need of nitrogen. If the same result is 

 obtained by adding phosphates, the soil is deficient in phosphorus. 

 If the addition of only one element is not sufficient to secure the 

 highest yield, then the experiments are carried out with cc:..- 



