Some species are entirely parasitical on other lichens (e.g.
A very remarkable instance of an acquired means of protecting a wound against parasitical invasion is to be found in granulations.
A plant or animal in perfect health is more resistant to parasitical invasion than one which is ill-nourished and weakly.
Filamentous diatoms may be mounted like ordinary seaweeds, and, as well as all parasitic algae, should whenever possible be allowed to remain attached to a portion of the alga on which they grow, some species being almost always found found parasitical on particular plants.
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