"I greatly enjoyed my microscopic work," said Percy, "and still more the work in the chemical laboratory where we finally learned to analyze soils, to take them apart and see what they contain,--how much nitrogen how much phosphorus, how much limestone, or how much soil acidity, which means that limestone is needed. Then I also enjoyed the work in the pot-culture laboratory, where we learned not to analyze but to synthesize; that is, to put different materials together to make a soil. Thus, we would make one soil and put in all of the essential plant food elements except nitrogen, and another with only phosphorus lacking, and still another with both nitrogen and phosphorus present, and all of the other essential elements provided, except potassium, or magnesium, or iron. These prepared soils were put in glass jars having a hole in the bottom for drainage, and then the same kind of seeds were planted in each jar or pot. Some students planted corn, others oats or wheat or any kind of farm seeds. I grew rape plants in one series of pots, and I have a photograph with me which shows very well that all of the plant food elements are essential. "You see one pot contained no plant food and one was prepared with all of the ten essential elements provided. Then the other pots contained all but one of the necessary soil elements, as indicated in the photograph." "Why, I never saw anything like that," said Mrs. Thornton. "But I have many a time," said her husband, "right here on this old 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?"