v.] ACTION OF PHOSPHORIC ACID 139 



proportion of grain to straw being raised from 336 to 

 36-2. In the dry year the phosphoric acid so hurried 

 on the premature ripening of the grain that the yield 

 declined from 8-4 to 77 bushels, and the proportion the 

 grain bore to the straw similarly fell from 844 to 67-3 

 per 100 of straw. 



The action of phosphoric acid on the plant is not 

 confined to its ripening effect ; it stimulates the early 

 development of the young seedling to a remarkable 

 extent. Farmers are well acquainted with the good 

 start that any crop gets when manured with super- 

 phosphate ; indeed, it is often used merely to secure a 

 better plant, though with little expectation of otherwise 

 increasing the yield. More than sixty years ago this 

 had been noticed by the late Sir John Lawes ; and in 

 one of his earliest papers on " Turnip Culture " in 1847, 

 he writes : " Whether or not superphosphate of lime owes 

 much of its effect to its chemical actions in the soil, it is 

 certainly true that it causes a much enhanced develop- 

 ment of the underground collective apparatus of the 

 plant, especially of lateral and fibrous root." For this 

 statement he was vigorously attacked by Liebig, but 

 some experiments, which are still in progress, show that it 

 was the result of sound observation and that in some 

 way or other phosphoric acid does stimulate the root 

 development of the young plant. Barley seedlings, for 

 example, grown in water cultures without, or with a 

 minimal amount of, phosphoric acid develop practically 

 no root, whereas when they are nitrogen or potash 

 starved the root growth will be proportional to that 

 of the rest of the plant. Both in the field and in 

 pot experiments the phosphoric acid has a great effect 

 in promoting the formation of adventitious buds, 

 so leading to the tillering of the plant. To what 

 extent this stimulus to root growth is brought about 



