"Very good, Jack," said Becker.

"Suppose," continued Ernest, "that the ground in the neighborhood of
your plant was of two very opposite qualities, that on the right, for
example, damp, rich, and spongy; that on the left, dry, poor, and
rocky; you would find that the roots, after growing for a time up or
down, as the case might be, will very soon change their route, and
take their course towards the rich and humid soil."

"And quite right too," said Willis; "they prefer to go where they will
be best fed."

"If, then, these roots stretched out to points where they would
withdraw the nourishment from other plants in the neighborhood--how
could you prevent it?"

"By digging a ditch between them and the plants they threaten to
impoverish."

"And do you suppose that would be sufficient?"

"Yes, unless the plant you refer to was an engineer."

"Therein lies the difficulty. Plants are engineers; they would send
their roots along the bottom of the ditch, or they would creep under
it--at all events, the roots would find their way to the coveted soil
in spite of you; if you dug a mine, they would countermine it, and
obtain supplies from the opposite territory, and revenge themselves
there for the scurvy treatment to which they had been subjected. What