1907.] PUBLIC DOCUMENT — No. 33. 189 



moisture. This was quite noticeable in the experiments, in- 

 asmuch as the ashes act like a sponge and water is retained 

 to quite an extent by them ; while in the sand no such absorp- 

 tion takes place, as is readily shown by the top layers of the 

 coarse sand becoming dry, — so much so at times that seed 

 germination was seriously interrupted. For this reason it was 

 impossible to maintain the same relative degree of moisture 

 in the various strata in the sand boxes as in the ashes. Since 

 ashes were more porous and spongy, the difference in the 

 amount of moisture in the various strata was less marked, 

 and there was no difficulty in maintaining enough moisture 

 for germination in the coarse particles of coal ashes. 



The influence of variation in the soil moisture cannot be 

 eliminated in comparative experiments with soils of different 

 texture, since the capillarity of the different grades of soils 

 is by no means the same ; neither is the amount of water 

 which the seeds and seedlings received under these conditions 

 identical. 



Some parallel experiments were undertaken in shallow 

 plates, containing about three-fourths inches of coal ashes, 

 having the same range in the size of particles as in the 

 previous experiment, with somewhat similar results. In the 

 plate experiments the difference in the amount of moisture 

 due to the difference in the capillarity was considerably mod- 

 ified, since the substratum was so shallow that the seedlings, 

 after they had become mature to a certain degree, could obtain 

 jDractically the same amount of water from each type of par- 

 ticles, providing evaporation was checked, thus preventing 

 stimulation which would arise from the difference in the water 

 supply, although the water in the plates containing the coarse 

 particles would be more largely confined to the lower strata. 

 Soil texture and water supply are intimately associated, and 

 this has led some to believe that water constitutes the ruling 

 element in the soil in crop production. Respiration is also 

 an important function in plants, for which process oxygen is 

 necessary. When plants are deprived of oxygen they cease 

 to grow, and seeds will not germinate. 



It is important that roots be supplied with air for respira- 

 tion, as is shown by aeration experiments ; and in the experi- 



