256 Report of the Department of Chemistry of the 



luxuriance even when the ingredients of the ash differ in quantity 

 and proportions to a marked degree. 



Students of plant nutrition cannot fail to observe that the com- 

 position of the ash of the same species of plant varies greatly accord- 

 ing to the locality in which the plant is grown and the methods 

 used. 



In view of these facts it is proper to inquire whether there is a 

 determinable minimum proportion of certain ingredients in the 

 dry matter produced by agricultural plants. In other words, what 

 is the essential minimum of phosphoric acid or potash which must 

 be available to a plant in order that maximum growth may be 

 secured? 



An attempt has been made to throw light on this question by 

 carefully controlled experiments in which several species of plants 

 were grown under such conditions that all the needed elements of 

 plant growth but one were available in great abundance, this one 

 element being supplied to different lots of plants in progressively 

 increasing quantities. Such experiments were continued during 

 three seasons. 



PLAN AND DETAILS OF EXPERIMENTS. 



The experiments in question were carried on in the Station forcing 

 houses during the winters of 1900-1, 1901-2 and 1903-4. The 

 experimental plants included barley, peas, tobacco, tomatoes, buck- 

 wheat, rape, and turnips. These were grown in boxes fifteen inches 

 square and six inches deep, which were filled as follows: 



1900-1 Quartz sand and coarse quartz for 



drainage weighing in all about 50 pounds. 



1901-2 Quartz sand running through sieve 



forty meshes to the inch 31 pounds. 



Fine drainage 4 



Coarse drainage 8 



Ground sphagnum moss .93 pounds. 



1903^ Filling the same as in 1901-2. 



The moss used, which constituted about 3 per ct. of the mixture, 

 was that which had grown under water. It was air dried, sticks and 

 foreign matter were removed, and then it was coarsely ground. 

 On analysis it was found to contain .0984 per ct. of potash (K 2 0). 

 Of P 2 5 there was present only a trace. 



As a source of plant food Kahlbaums c.p. chemicals were used, 

 including the tri-calcium phosphate from which the acid phosphate 

 was made. 



The experimental boxes included two general series, those in 

 which graduated amounts of phosphoric acid were used, and those 

 in which the same plan was followed with potash. 



