AGRICULTURAL EXPERIMENT STATION. 17 



Hedonda phosphate show a superior value, which, though evident, 

 ■was not marked. 



There are two explanations which may be suggested for this fact: 

 (a) The action of the citrate solution is not even an approximate 

 measure of the root action of plants, or (b) the dehydrated phos- 

 phates of iron and alumina revert to a hydrated and less available 

 condition after entering the soil. 



(4) The eight species of plants employed in these experiments 

 showed greatly unlike ability to appropriate phosphoric acid from 

 the water-insoluble phosphates. The differences in this respect 

 were striking. From almost the very earliest period of growth, the 

 two varieties of turnips appeared to feed nearly as freely upon the 

 Florida rock as upon the dissolved Florida rock, whereas the barley, 

 corn, potatoes and tomatoes derived but little if any benefit from the 

 water-insoluble phosphates until during the more advanced stages 

 of growth, and even then the benefit was not nearly so marked as 

 with the cruciferous plants. 



The leguminous plants, viz. peas and clover, appeared to occupy a 

 position between the cruciferous and graminaceous plants, showing a 

 very material increase of early development due to the water-in- 

 soluble phosphates. 



The facts so far observed suggest that this difference in feeding 

 power which these plants exhibited is more than a difference between 

 single species and relates to groups of species. 



(5) The ability to ax^propriate water-insoluble phosphoric acid ap- 

 peared with some species of plants to greatly increase as the plants 

 developed. 



While the turnips and ruta-bagas fed freely upon the crude 

 Florida rock even in the earlier stages of growth, it was observed 

 that not until after some weeks did the clover, tomatoes and in one 

 case the corn, begin to make any perceptible use of the water-nsol- 

 uble phosphates. 



The photographs showing £he clover in two stages of g-rowth illus- 

 trate the above statement very clearly. This observed increase of 

 feeding power as the plants matured, so that they fed upon the 

 crude ground rock, especially the clover, suggests that the crii.de 

 ground phosphates may be made a cheap and useful source of phos- 

 phoric acid in grass fields, and on the other hand the inability of 

 several species, notably certain of the gramineae and solanaceae, to 

 use the water-insoluble phosphates freely in the earlier periods of 

 growth, emphasizes the wisdom of using chiefly water-soluble 

 phosphoric acid upon hoed crops, especially where early maturty is 

 essential. 



The following table shows very clearly the relation of growth of 

 the several species when fed with the different forms of phosphoric 

 acid. 



