AGRICULTURE AND RURAL ECONOMY. 365 



Phosphoric Acid as the Food of Plants. 



Dr. Petersen, of the experiment station at Regenwalde, in 

 Germany, reports some experiments in water-culture, with 



the object of determining what proportion of phosphoric acid 

 is essential to the best development of the oat plant. The 

 maximum yield was obtained in solutions which, besides 

 the other essential ingredients of plant-food, furnished 0.071 

 grams of phosphoric acid to each plant. Plants grown in 

 these solutions yielded each, on the average, 197 seeds, and 

 in the whole plant 10,497 grams dry substance, or 316-fold 

 the weight of the seed. In solutions exactly similar, except 

 that they furnished only half as much phosphoric acid, the 

 plants averaged only ninety-four seeds and 3508 grams dry 

 substance, or 114-fold the weight of the seed. 



The results of these experiments agree essentially with 

 those of a number of similar ones reported some time since 

 by AVolff. Both investigators found that when the phos- 

 phoric acid did not exceed 0.33 per cent, ot the whole 

 weight of the dry substance of the plant, the latter suffered 

 in the development of all its parts. On the other hand, ex- 

 cess of phosphoric acid did no harm, but seemed rather to 

 favor a better development of seed. Wolff calls attention 

 to the difference between phosphoric acid and nitrogen in 

 this respect, the latter, as is well known, having a tendency, 

 when applied in excess, to injure the development of the 

 seeds of cereal grains and cause an excessive growth of stalk, 

 and often lodging of the grain. In this view, it is clear why 

 the excessive use of phosphates which obtains in some farm- 

 ing districts has not proved injurious. 



Lime as Plant -Food. 



Boehm has studied the plant-nourishing value of calcium 

 salts by exDeriments on scarlet-runner beans. He concludes 

 that mineral matter is absolutely required for the young 

 plant in order that it may avail itself of the excess of nour- 

 ishment stored in the seeds, the mineral matter in the seeds 

 being insufficient for this purpose; that without lime salts 

 the growing plants soon wither away and die; and that, 

 finally, lime salts do not participate directly or indirectly in 

 the formation of starch. He also shows that plants may ab- 



