"The salmon is one of the most important food fishes of the country," the professor said rebukingly, "and it is as important for us to know
all about its habits as it is to know about the way a grain of wheat grows."
"I hadn't thought of that," Colin said, a little shamefacedly. "I suppose everything really is important, no matter how small."
The professor smiled at him.
"If you have much to do with studying fish," he said, "or, indeed, with any kind of science, you will find out it is always the little things that tell the story. Take the grain of wheat again. If one kind of wheat ripens two days earlier on an average than another kind, you might think that so small a difference wouldn't be of great importance, but those two days might—and often do—make the difference between a good crop and one which is frost-bitten and spoiled."
"That's a lot easier to see," agreed the boy. "But, sir," he objected, "you can pick out one little bit of a field and work on that, and it will 'stay put.' Fishes wander all over the place."
"We want them to do so, my boy," was the reply.
"How can you work on separate fish? One looks so like another!"
"And for that very reason we're going to tag them."