In an a legal sense you may be right, that quote would legally be considered as "hearsay" and therefore legally inadmissible as testimony in a court of law. Moreover, the use of quotation marks to indicate this was a actual quotation of Einstein's actual words, may be inappropriate in this case also as the actual sentence was perhaps a loose translation of Einstein's words by Barnett.. Thus, in a technical sense, I agree with you. However, is it really relevant as to IF Einstein actually said something like that in conversation with Barnett. How would Barnett be able to cite specific substantive phrases, such as "common sense", " deposit of prejudices", "prior to the age of eighteen", if he had not personally witnessed Einstein saying something to that effect? If Barnett's recollection or interpretation of Einstein's actual words are suspect, then would that not disqualify the entire statement of Barnett as "fruit of the poisonous tree"? The legal result is inadmissability of the entire tainted statement. Note the use of the term "poisonous tree" over the use of the term "poisoned tree". There is a subtle but profound implication in the use of that specific phrase. Are you prepared to call Barnett (the Tree) incompetent or dishonest in his interpretation of what Einstein personally conveyed to him. If so, are you prepared to dismiss Barnett as a "poisonous tree"?