Cover illustration: Stigmas from Senecio squalidus (Asteraceae): (A) stained for the presence of peroxidase; (B) stained with tetramethylbenzidine (TMB) to show the presence of hydrogen peroxide; (C) stained with the fluorescent probe dichlorodihydrofluorescein diacetate (DCFH2-DA) to show the presence of reactive oxygen species. (See McInnis et al., pp. 1835–1846.)
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