"Nat Poole, what are you up to!" cried Dave, indignantly, and, leaping forward, he caught the other youth by the shoulder and whirled him around. "You let Professor Potts alone!"
"Dave!" cried the professor, and his voice showed his joy. "Oh, I am glad you came. That young man has been teasing me for over a quarter of an hour, and he just covered me with that spray for the peach-tree scale."
"What do you mean by doing such a thing?" demanded Dave. "Give me that syringe." And he wrenched the article from the other youth's grasp. He looked so determined that Nat became alarmed and backed away several feet.
"Don't you—you—er—hit me!" cried the money-lender's son.
"What a mean piece of business," observed Roger, as he came up, followed by Phil. "Nat, you ought to be ashamed of yourself!"
"Oh, you shut up!" grumbled Nat, not knowing what else to say.
"I always thought you were a first-class coward," put in Phil. "Now I am sure of it."
"This is none of your affair, Phil Lawrence!"
"I should think it was the affair of any person who wanted to see fair play," answered the shipowner's son.
"Nat, you take your handkerchief and wipe off Mr. Potts's clothes," said Dave, sternly.