AGRICULTURAL EXPERIMENT STATION. 11 



change on standing whereby the phosphate gradually becomes less 

 soluble in the citrate solution. 



Ninety-six boxes were used, twelve for each kind of plant. In the 

 first box the acid rock was used; in the second, the crude rock; in 

 the third,' the phosphate of iron and alumina; in the fourth, no phos- 

 phate. The next four boxes were treated in the same manner, and 

 so on to the end. Thus it will be seen that for each kind of plant 

 there were three boxes which received the same treatment. 



Twenty grams of the crude Florida rock, containing 6.576 grams 

 total phosphoric acid, were used for a single box. Of the other phos- 

 phates such quantities were used as contained the same total amount, 

 6.576 grams, of phosphoric acid. 



To each box were also added: Ten grams sodium nitrate; five 

 grams potassium chloride; five grams magnesium sulphate. To the 

 boxes containing the phosphate of iron and alumina and to those 

 containing no phosphate were also added ten grams calcium sul- 

 phate. All these materials were carefully mixed with the screened 

 sand before it was placed in the boxes. 



The clover and barley were planted in seven rows of seven plants 

 each, or forty-nine plants to each box. The peas were thinned to 

 nine plants. Of the other plants, four were grown in each box. All 

 the conditions were made as uniform as possible in order that what- 

 ever differences were observable might fairly be attributed to the 

 differences in the phosphates used. The seed was carefully selected, 

 that only being used which was well formed and of uniform size. Such 

 leaves as ripened before the plants matured were removed, dried and 

 added to the plants when harvested. No attempt was made at pollr 

 nation. As very few insects were present during' the growth of 

 the plants, the fruiting,as niig'ht have been expected,was very irregu- 

 lar. 



When the most advanced plants of each species had reached their 

 highest development, all the plants of that species were harvested. 

 The plants were carefully dried, weighed and ground. The moisture 

 was determined in each sample and the water free weights calculated. 



The experiments were continued through three periods. In the 

 first period the barley matured its heads, and many of the pea-pods 

 were well filled. The second period extended through the shortest 

 days of the winter, when the lack of sun and the lower temperature 

 were unfavorable to the best development of the corn and tomatoes. 

 The third period was made shorter than the others, and none of the 

 plants reached their full development. 



At the close of the second period the clover was not harvested, 

 but was allowed to grow on through the third period. 



All but one of the photographs from which the accompanying cuts 

 were made were taken at the close of the second period. The second 

 cut of the clover is from a photograph made at the end of the third 

 period, and represents the same plants as those shown in the pre- 

 ceding illustration. 



