"Not altogether; there are certain plants which live on other plants and get sustenance from them, just as some insects attach themselves to animals and live on them."
"There is one thing I could never understand," remarked Tom, "and that is, why the sap of the trees goes upwardly."
"I shall try and answer that question by ask[p. 67]ing another. If you put the end of a piece of blotting paper in water, what causes the water to travel along to the other end?"
"That is just as much a mystery," he replied.
"But as you know that to be so, because you can see the process, it will enable me to explain the principle of the movement of the sap. A wick in a lamp becomes saturated and the oil travels upwardly as long as the upper end is burning; but as soon as the light is put out the oil ceases to creep toward the burned end."
"But in the case of a tree there is nothing to do that same thing."
"That is what the sun does. It shines on the leaf, and absorbs the sap, or portions of it, and the sap tries to move upwardly to again moisten the dried pores of the wood."
"I always thought the sap moved upwardly, because the tree was alive."
"The blotting paper and the wick are not alive, are they? Still, you see the same process going on. This is due to what is termed capillary attraction. Suppose you take two tubes, one larger than the other, each open at both ends, and stand them in water. The water will rise in the tubes above the surface of the water outside, and the height it rises depends on the inside diameters of the tubes. The smaller the bore the higher will the water go up. So with the pores in the wood. They are very small, and thus the water moves to the greatest heights."
It was now a question of the greatest importance to set up their home at the most desirable[p. 68] point. The Chiefs, together with John and Blakely, had numerous conferences with the Professor, on this subject. Many things had to be taken into consideration.