168 PLANT GROWTH 



plied on small adjoining areas in the fall you are almost sure 

 to see differences during the following summer. Other ex- 

 periments will suggest themselves. When crops are grown 

 in rows, the treatment can be varied in much the same way, 

 as well as in varying the relative amounts of the different 

 elements. One can even omit nitrogen, potassium, or phos- 

 phorus from some of the plants. The results should be 

 judged by the yield and by the characteristics of color, leaf 

 size, and stem growth. If possible certain areas should have 

 normal or no treatment for comparison as checks, with any 

 type of experiment. The tabulation on page 169 should be 

 consulted. Garden soils are seldom so deficient in any ele- 

 ment as to show clearly the deficiencies described in the 

 table, but the contents of artificial solutions made by adding 

 salts to water can be accurately controlled. This experimeiit 

 may be carried out by growing the plants directly in the 

 water solution or by growing them in washed sand to which 

 the water solution is added. 



The photographs of buckwheat and cowpeas (Plates XI 

 and XII) show the results of simple experiments in defi- 

 ciency symptoms. Plants grown in clean sand with solutions 

 added are compared with those grown in soil as checks. 

 Color photographs of deficiencies are often shown in maga- 

 zine advertisements for fertilizers. In performing either of 

 these experiments a solution is made with ten of the eleven 

 essential elements. The plant will be able to grow normally 

 until it has used the supply of the omitted element from the 

 seed and from the impurities of the other salts. Because of 

 the difficulty of getting pure salts, plants grown in solutions 

 lacking boron, zinc, and other elements used in very small 

 quantities show deficiencies barely detectable. Those grown 

 in solutions lacking nitrogen and other elements required in 

 larger amounts show a growth proportional to the amount 

 used in the plant and the amount stored in the seed. The 

 cowpeas lost their leaves sooner without nitrogen. A small 



