farm; I don't know what's lacking, of course, but some years I've
thought most everything was lacking. But, according to this
pot-culture test, you can't raise any crops if just one of these ten
elements is lacking, no matter how much you have of the other nine;
and it seems to make no difference which one is lacking, you don't
get any crop. Is that the fact, Mr. Johnston?"

One pot with no plant food, and one with all the essential elements
provided, and still others with but one element lacking. All planted
the same day and cared for alike.

"Yes, Sir," Percy replied. "Where all of the elements are provided,
a fine crop is produced, but in each case where a single element is
omitted that is the only difference, and in some cases the result is
worse than where no plant food is supplied. It seems to hurt the
plant worse to throw its food supply completely out of balance than
to leave it with nothing except what it draws from the meager store
in the seed planted. Of course all the pots were planted with the
same kind of seed at the same time, and they were all watered
uniformly every day."

"Those results are very striking, indeed," said Miss Russell," but I
suppose one would never see such marked differences under farm
conditions?"

"Only under unusual or abnormal conditions," Percy replied, "but the
fact is that as a very general rule our crop yields are limited
chiefly because the supply of available plant food is limited.
Sometimes the clover crop is a complete failure on untreated land,
while it lives and produces a good crop if the soil is properly