How has the court interpreted the Fourth Amendment in a search of a man's backpack by a police officer?

Here, defendant acknowledges that Griffin was justified in stopping him while he was riding his tricycle at night without the required lighting. Defendant also concedes that the officer was justified in further detaining him when he noticed a rifle scabbard attached to the tricycle. He contends, however, that Griffin exceeded constitutional limits when, after ascertaining that defendant was entitled to possess the rifle which remained in the police car, and without defendant's consent, he reached into the pocket of defendant's jacket, where he found a marijuana pipe and a small quantity of marijuana. Defendant implicitly acknowledges that that discovery, followed by defendant's admission that there were 10 grams of marijuana in his backpack, provided justification for extending the search, leading to the discovery of the additional and more significant evidence in the backpack. As the trial court reasoned and defendant does not dispute, the sole issue is whether the search of the jacket pocket was reasonable. We assume, as defendant contends, that if the initial search of the jacket pocket exceeded Fourth Amendment limits, all of the evidence obtained from defendant's backpack as well as from his pocket would be subject to exclusion as "fruit of the poisonous tree." (Wong Sun v. United States (1963) 371 U.S. 471, 488.)