introduced him to the soil physicist and the soil chemist. Percy was
greatly interested in the various lines of work in progress and
gladly accepted an invitation to return after lunch and become
better acquainted with the methods of investigation used.

In the afternoon the physicist showed him how the soil water could
be removed from an ordinary moist soil by centrifugal force, and the
chemist was growing wheat seedlings in small quantities of this
water and in water extracts contained in bottles. The seedlings were
allowed to grow for twenty days and then other seedlings were
started in the same solution and also in fresh solution, and it was
very apparent that in some cases the wheat grew better in the fresh
solutions.

The chemist explained that he also analyzed the soil solutions and
water extracts from different soils and that there was no relation
between the crop yields and the chemical composition of the soils.

"But it seems to me," said Percy, "that your analysis refers to the
plant food dissolved in the soil water only at the time when you
extract it. How long a time does it require to make the extraction?"

"As a rule we shake the soil with water for three minutes and then
it takes twenty minutes to separate the water from the soil. This
gives us the plant food in solution and with the addition of more
water the nitrates, phosphoric acid, and potash in the soil
immediately dissolve sufficiently give us a nutrient solution of the
same concentration as we had before. Thus there is always sufficient
plant food in the soil so long as there is any of the original
stock."