78 



In considering the causes of the differences noted between the 

 two systems of management we can do little more than state the 

 hypotheses which seem to account for the results. The experiment 

 is by no means concluded and definite reasons cannot be advanced 

 until all the proof is in. Yet it seems to me I am warranted in offer- 

 ing the following hypotheses : 



First. Plant food is more available in the tilled plot than in the 

 sod plot. That there is an abundance of the plant food necessary for 

 the welfare of the trees and the production of crops in both plots is 

 certain. For the trees in the tilled plots showed in all respects, 

 good feeding, and such trees in the sod-mulch' plots as could get anv 

 considerable portion of their roots in soil where there were no 

 grass roots, likewise seemed to be well fed. INIoreover, two of the 

 chief elements of plant food, potash and phosphoric acid, were 

 added to a part of the trees in each plot for three successive sea- 

 sons and without appreciable results in either case. It is evident 

 that there is plenty of food in the sod land but for some reason it is 

 not available to the apple trees. The trees are starving in a land of 

 plenty. 



Second. The sod-mulch does not conserve moisture as well 

 as tillage. The chief study in the Auchter orchard for the summer 

 of 1907 was that of the water content of the soil in the two plots. 

 One hundred twenty-eight samples of soil were taken at different 

 times during the summer and under conditions safe-guarded in every 

 way possible to determine accurately the amount of moisture in the 

 soil. The analyses showed, approximately, that the water content 

 in the tilled soil during the past summer, was twice as great as in 

 the sod plot, thereby substantiating what has long been claimed that 

 tillage is a better means of conserving moisture than mulching. 



Trees must have water. If an apple tree bears ten barrels of 

 fruit, there are about eight and one-half barrels of water in the tree's 

 output. In a full grown apple tree it is estimated that the total leaf 

 area is about 1,000,000 square inches. i\Ir. F. C. Stewart of the 

 Geneva Station has counted the stomata or pores on a square inch 

 of the apple leaf and finds that a fair average is about 150,000 per 

 square inch. Or for the leaf area of the whole tree, 150,000,000,000 

 pores. Now to supply the demands of its ten barrels of apple chil- 

 dren while these mo,ooo,ooo,ooo pores are constantly giving mois- 

 ture is enough to drive a tree to drink and the apple tree becomes 

 a hard drinker. When in the heat and drought of summer, the 

 apple tree is compelled to share its scant supply of water with the 

 thirsty horde of hangers-on found in an orchard sod the trees 

 must sufl:*er. Still further, a diminished water supply entails a cut- 

 ting ofi:" of the food supplv. Plant food enters the tree as a solu- 

 tion and an apple tree suffering from lack of water as a necessary 

 consequence suffers from a lack of food. A thirsty plant is a 

 hungry plant. 



Third. The sod-mulch soil is less well aerated. In the ex- 

 periments we are carrving on I have not attempted to secure evi- 

 dence on this point. It is obvious that sod interferes with the air 

 supply in the ground beneath it and it is not hard tQ believe that such 



