CLASSIFICATION OF PLANTS ON THE BASIS OF PARASITISM

Abstract

The rapidly expanding field of plant parasitology increases the need of a classification of parasites. It is hoped that this attempt to classify some of the categories of parasites will be of value in the consideration and teaching of plant pathology. The necessity for securing greater clearness of understanding and description of parasitism is the purpose of this compilation. The interrelationships of organisms, including parasites, are considered by McDougall (i6) to be forms of symbiosis. Parasites which cause hyperplasia, hypertrophy and fasciations, and the fungi which cause animal diseases, exhibit numerous physiological adaptations. Parasites penetrate their hosts through stomata or wounds or by haustoria forced through the cuticles. After entering, parasites occupy subcuticular, tracheal, parenchymatous, intercellular, intracellular and other positions. These various characteristics of parasites are not used as a basis of classification in the present paper. Parasites are here grouped according to analogies in their life cycles and in the type and degree of their parasitism; phylogeny is not considered. The general arrangement of the groups is based on their specialization in parasitism. The names of some organisms are given to exemplify the classes of parasites. A few new terms are applied to categories for which there are no terms in existence or general use. This physiological classification is based on the following definition of a parasite: A parasite is an organism which lives in or attached to some other species of living organism from which it secures part or all of its food material in the form of living matter. Plants are classified into the following main groups: