The use of the term "chemical defenses" implies active evolution of toxic, noxious, or unpalatable compounds for purposes of deterrence. In the case of animals, the evolution and elaboration of glands specifically designed to aid delivery of noxious substances seems evidence enough of purpose. Additional behavioral or morphological adaptations, e.g, aposematism, often provide convincing evidence that the use of compounds is intimately related to protection from potential consumers (Kerfoot 1982, Scrimshaw and Kerfoot 1987). Palatability tests are used to confirm initial impressions and to quantify relative vulnerability. Unfortunately, these obvious clues are often absent in macrophytes. The mere presence of noxious compunds is not sufficient to demonstrate defensive design, per se. Three levels of proof seem necessary: (a) Are noxious substances present in tissues? (b) Are they of sufficient quantity to influence palatability and hence herbivory? and (c) Have they evolved specifically as a defense against herbivory?