"Oh, Papa's just fooling," said Prue. "Why, no," said the Chief Gardener, "don't you see them. There is a whole drove of cows," and he pointed to some little green bug-like things that clustered on the tips of his pea-vines. The children looked closely and then turned to him to explain. "There are some ants there, too," said Davy. "They are crawling up and down." "Yes," said the Chief Gardener. "They own the cows. The cows are those green things--aphides, they are called, and the ants milk them. Look very carefully now." Prue and Davy watched and saw an ant go to one of the green insects and touch with its bill first one, and then the other, of two little horns that grew from the aphid's back. And then the ant went to another aphid, and did the same thing. Then they saw that tiny drops of fluid came from the ends of these tiny green horns. "That," said the Chief Gardener, "is honeydew, or ant's milk. The ants are very fond of it, and wherever you find these aphides, you will find ants, milking them. In fact, I believe the ants keep these aphides during the winter in some of their houses, and drive them in the spring to tender green feeding-places like these pea-vines, so that the milk will be sweet and plentiful. I have heard that different families of ants have different droves of cows, and fight over them, too." The children were very much interested in all this, and watched the ants run up and down the vines and milk their cows. Then the Chief Gardener said, "I'm sorry, but I'm afraid we'll have to get rid of these. They are very bad for young plants, and ants are, too. They suck the juice, and ruin them. I must give them a mixture." He went into the basement and cut up a few ounces of whale-oil soap, and dissolved it in hot water. Then when it was cool and weakened, he sprinkled the pease with it. The next day all the cows were gone, and most of the ants. But about a week later, just after a shower, there they were again, and the Chief Gardener said that the ants must have driven up a new herd. So he had to sprinkle them again, and even once more before the end of the month; and while he was sprinkling, he sprinkled the little gardens, too, for whale-oil soap when it isn't used strong enough to hurt the young plants is a fine thing for little gardens, and big ones, too. III THERE ARE MANY WAYS OF PRODUCING SPECIES THERE were a good many rains in May. The weeds grew and grew, and it was hard to keep them down when it was wet and warm, and the plants were still so small. Prue and Davy had to get down close and pull them out carefully with their fingers, and this left the little green rows so straight and trim, and the earth smelled so nice when the sun came out warm, after a shower, that the children grew happy in the work, and wanted to plant new things almost every day.