“Now taste the water in the glass outside the skin,” said Uncle George. “It was fresh water when we put it in, wasn’t it?” Frank did so. Tom tasted it too. Both boys declared that it was now salt. “Where did the salt taste come from?” their uncle asked. “It must have come through the skin,” said Tom. “Then some of the salt water in the thistle tube has passed through the skin into the glass; and some of the fresh water in the glass has passed through the skin into the thistle tube. Can you tell me any more?” Frank thought for a little while and then said, “Oh yes, more fresh water than salt water has passed through the skin, because the salt water is now far up the tube.” “Quite right, my boy. Now let us look at the small bottles. The skin on the one filled with brine is swollen out like a ball, while the water in the dish tastes salt. The skin of the other is drawn far in, showing us that much of the fresh water which it contained has passed out. If you taste the water in this bottle, you will find that a very little of the brine in the dish has passed into it through the skin. “Now what we learn from these things is really this—that when two liquids, a heavy and a light one, are separated by a thin skin, they _both_ pass through the skin. The heavy liquid passes through slowly, and the light liquid passes through quickly.” Uncle George then placed some small seeds on a piece of wet blotting-paper. He turned a glass tumbler upside down, and placed it over them. “We will leave these for a few days,” he said. Questions and Exercises. 1. Boil some river-water in a flat dish until all the water is gone. Do the same with some sea-water, or, if this is not at hand, make some brine. Examine the two dishes, and tell what you see. 2. Take a glass gas chimney, and tie a piece of bladder, or parchment, over one end of it. Half fill it with sugar and water. Now place it with its tied-up end bottommost in a tumbler of clear cold water. After an hour or so taste the water in the tumbler. What have you to say about it? 3. What takes place when brine and clear water are separated from one another by a piece of skin (parchment)? [Illustration: A Box of Mustard Seeds.] II.—HOW PLANTS TAKE FOOD FROM THE SOIL (2). A whole week went by before Uncle George was ready for the next lesson. At last he called the children and said to them—“Tom, will you please fetch me the seeds which we put on the wet blotting-paper under the tumbler? Frank, bring me two leafy branches from a rose-bush in the garden; and, Dolly, please fetch two glasses from the kitchen.” Now there was nothing the children liked better than to help their Uncle George, and all three rushed off at once to do his bidding.