<P> Other defensive strategies used by plants include escaping or avoiding herbivores in any time and / or any place, for example by growing in a location where plants are not easily found or accessed by herbivores, or by changing seasonal growth patterns . Another approach diverts herbivores toward eating non-essential parts, or enhances the ability of a plant to recover from the damage caused by herbivory . Some plants encourage the presence of natural enemies of herbivores, which in turn protect the plant . Each type of defense can be either constitutive (always present in the plant), or induced (produced in reaction to damage or stress caused by herbivores). </P> <P> Historically, insects have been the most significant herbivores, and the evolution of land plants is closely associated with the evolution of insects . While most plant defenses are directed against insects, other defenses have evolved that are aimed at vertebrate herbivores, such as birds and mammals . The study of plant defenses against herbivory is important, not only from an evolutionary view point, but also in the direct impact that these defenses have on agriculture, including human and livestock food sources; as beneficial' biological control agents' in biological pest control programs; as well as in the search for plants of medical importance . </P> <P> The earliest land plants evolved from aquatic plants around 450 million years ago (Ma) in the Ordovician period . Many plants have adapted to iodine - deficient terrestrial environment by removing iodine from their metabolism, in fact iodine is essential only for animal cells . An important antiparasitic action is caused by the block of the transport of iodide of animal cells inhibiting sodium - iodide symporter (NIS). Many plant pesticides are glycosides (as the cardiac digitoxin) and cyanogenic glycosides which liberate cyanide, which, blocking cytochrome c oxidase and NIS, is poisonous only for a large part of parasites and herbivores and not for the plant cells in which it seems useful in seed dormancy phase . Iodide is not pesticide, but is oxidized, by vegetable peroxidase, to iodine, which is a strong oxidant, it is able to kill bacteria, fungi and protozoa . </P> <P> The Cretaceous period saw the appearance of more plant defense mechanisms . The diversification of flowering plants (angiosperms) at that time is associated with the sudden burst of speciation in insects . This diversification of insects represented a major selective force in plant evolution, and led to selection of plants that had defensive adaptations . Early insect herbivores were mandibulate and bit or chewed vegetation; but the evolution of vascular plants lead to the co-evolution of other forms of herbivory, such as sap - sucking, leaf mining, gall forming and nectar - feeding . </P>

What type of herbivore would leaf hairs (fuzzy leaves) defend against as compared to large thorns