104 THE APPLE 



for some of the divergence of opinion. No marked effect either 

 way has yet appeared in the author's apple experiments, though 

 perhaps the tendency has been to hasten maturity. 



It is worthy of note that where nitrate of soda has been used 

 as nitrogen carrier in the Rothamsted * work, no sign of potash fail- 

 ure has been observed in twelve years. This is taken to indicate 

 that sodium liberates potash in the soil. 



While potash shows relatively little migratory tendency, it is 

 nevertheless subject to marked losses as the plants mature (see 

 the discussion of phosphorus). 



Calcium. The use of lime in agricultural practice is very old. 

 In many soils it is an important factor, and, because of the large 

 demand of most plants for it, its need is often felt very early. 

 The part that it plays in the nutrition of plants is variable — in 

 some soils it merely modifies environment, while in others its 

 action is physiological. Lime accumulates in plants chiefly in the 

 leaves, and to some extent in the wood. Etiolated, diseased, or 

 albino leaves contain much less lime than healthy green leaves, 

 the difference in amount sometimes being more than half. Since 

 it may be largely or entirely absent from young plant organs, it 

 does not seem to be essential to the young plants, but is useful in 

 certain special processes. In the older plants, however, it has 

 apparently acquired such importance in these special functions 

 that its absence may indirectly affect one or all of the vital 

 activities and thus obstruct metabolism. 



The special function that has been most clearly associated with 

 calcium is concerned with the solution and transfer of starch as 

 contrasted with the starch-building role of potash. The function 

 of lime in acid neutralization in plants is now considered less 

 essential than formerly, since the resulting calcium oxalates are 

 found to be absent in many plants. 



The functions of lime, in its soil-modifying capacity, are as 

 follows: (i) It corrects acidity. Most plants prefer slightly alka- 

 line soils, but the exact preference of the apple is not known. 

 (2) It liberates other nutrients. The liberation should not be too 

 fast, however, or losses may occur by leaching. This " whip " 

 action has sometimes been considered the only function of lime. 



1 The Rothamsted Experimental Station, Ilarpenden, England. 



