AGRICULTURAL, EXPERIMENT STATION. 15 



COMMENTS. 

 W. H. Jordan. 



It is often difficult, perhaps impossible in some instances, to so 

 display experimental data that they shall convey to the reader the 

 full significance of the results reached. This appears to be peculiar- 

 ly the ease with the forcing house experiments discussed on preced- 

 ing- pages by Mr. Merrill. The object of the investigation under dis- 

 cussion is a study of the ability, relatively and absolutely of certain 

 plants to appropriate phosphoric acid to their uses when presented 

 to them in various forms, or at least when applied to the soil in vari- 

 ous forms. 



These plants have been groAvn in a forcing house in a manner which 

 has been described, where it has been possible to observe them 

 through the various stages of development, and the writer by his 

 observations is convinced of certain facts which are not easily made 

 clear by a display of numerical data, either in a tabular or graphic 

 form. Even the photographic illustrations fail to show more than 

 one or two periods of growth. 



The purpose, therefore, of supplementing Mr. Merrill's clear presen- 

 tation of the facts reached is to emphasize his statements by a dis- 

 cussion based partly on numerical data and partly upon data which 

 may not be expressed in numbers. 



It is well to remark first of all, that this investigation may be 

 regarded from two standpoints; (1) From the plant food side, when 

 the prominent consideration is the availability of certain materials 

 as plant food, or (2) from the plant side, when the prominent consid- 

 eration is the absolute or relative ability of different species of 

 plants to obtain food from certain sources. We will discuss our 

 experimental data from both points of view. 



(1) The acid-rock or soluble phosphoric acid proved to be the most 

 available. 



This is true whether we base our judgment upon the early growth 

 of the young plants or upon the total growth made. 

 There was no instance in which the young plants fed by the 

 soluble phosphoric acid did not show a more immediate and generous 

 growth than when fed by the water-insoluble, and if we consider 

 only average results, the total growth was in all cases largest from 

 the soluble phosphoric acid though not greatly larger with certain 

 plants. If we consider the readiness with which any material is 

 appropriated by the very young plant as the crucial test of its avail- 

 ability, then the phosphoric acid used in a soluble form has a relative 

 value greater than is indicated by the growth of the plants during 

 a somewhat extended period of time. 



