New York Agricultural Experiment Station. 245 



There is no uncertainty about the conclusions to which the 

 above data point. The main fact shown is that under the con- 

 ditions involved the availability of a phosphate is quite as much 

 a matter of the kind of crop as of the form of combination of the 

 phosphoric acid. The three crops belonging to 'the grass family — 

 barley, millet and oats, grew luxuriantly in the acid phosphate 

 boxes but acquired insignificant amounts of phosphoric acid, 

 and made little growth, where the undissolved Florida rock was 

 used. In strong contrast to this are the results with cabbage and 

 rape (cruciferous plants) where the growth of dry matter from 

 the floats was in some cases as large as with the acid phosphate 

 and in no instance noticeably less than three-fourths as large. 

 The cruciferous plants absorbed phosphoric acid from the floats 

 in fairly generous quantities but not as much in proportion to the 

 growth of dry matter as from the acid phosphate. The Thomas 

 slag and Eedonda phosphate appeared to be quite available to 

 all crops, although the growth from those was, with a single ex- 

 ception, less with all species and in all the experiments than 

 from the acid phosphate. 



The striking and important fact developed by these experi- 

 ments, however, is the unlike capacity of different species of plants 

 to utilize a given source of plant food, or, to put the matter an- 

 other way, the unlike adaptability of a given soil environment 

 to meeting the needs of different species of plants. It is funda- 

 mental in all our reasoning about plant nutrition to understand 

 whether plants possess with different degrees of intensity what 

 may be called feeding power, or whether it is merely a question 

 of securing for a particular species what may be termed a 

 " sympathetic " soil environment. It is quite clear that plants 

 possess more or less selective power in taking up the chemically 

 available compounds with which the roots are in contact, and why 

 may not there exist differences in their reaction upon a given 

 compound in the way of preparation for absorption? 



It is certain that in these and previous experiments a given 

 compound is inert to one plant to a much greater degree than to 



