BOX EXPERIMENTS WITH I'lIOSJ'lIORl C ACID. 73 



Other plants. The failure of the Crnciferae to respond to ihc 

 acid rock furnishes a good illustration of a similar kind. The 

 Umbelliferse, though responding to the acid rock, seem to derive 

 no benefit from either the floats or Redonda, since neither of the 

 phosphates increase the yield above that obtained where no 

 phosphate was used. This is true both of the whole plant and 

 the roots. 



The alfalfa shows a strange indifiference to the precise form in 

 which the phosphoric acid is supplied. The crop was light 

 i;i every case, and the phosphoric acid already present in the bar- 

 ren soil used, seems to have sufficed for the slender product. 



STIMULATING EFFECT OF ACID PHOSPHATE IN THE EARLY 

 STAGES OF GROWTH. 



A report of this work would be incomplete if it failed to take 

 note of certain facts observed in the course of the experiment 

 which cannot be shown in the diagram, where only the final 

 results are given. 



Throughout the whole series of experiments the efifect of the 

 acid rock was marked, the plants receiving it in nearly every 

 case at once taking the lead, and keeping it to the end.. This 

 stimulating efTect upon the young plant is shown in the accom- 

 panying cuts of the immature clover and timothy. The horse- 

 beans furnish a marked exception to this rule, the more nearly 

 equal development being perhaps due to the large amount of 

 nutriment stored in the seed. When this supply was exhausted, 

 the phosphoric acid hunger manifested itself, the effect being 

 shown in the cut of the same plant at a later period. 



In by far the larger number of cases, especially with the 

 clover, timothy, turnips and ruta-bagas, the good effects of the 

 acid rock were more marked during the first few weeks of 

 growth than at a later stage, when the roots had become more 

 fully developed, and had begun to forage for themselves. This 

 fact, also, is shown in the cuts of the clover and timothy. It 

 would appear that the young plants feed but little upon the in- 

 soluble phosphates ; but that the organic acids present in the sap 

 of the roots exert a solvent action upon the insoluble phosphates 

 in the soil, gradually converting them into available forms. 





