Among the theories offered to explain how pathogenic organisms induce pathic events in plants the toxin theory has gained much support especially in recent years. According to this theory the disease syndrome is not induced by the pathogen directly but by toxins formed by the pathogen itself. The host reactions which have been ascribed to the action of such toxic secretions of the pathogen include: (1) vein clearing, (2) epinasty of leaves, (3) production of adventitious roots on the stem, (4) yellowing of leaves, (5) vascular browning, (6) production of gum in vessels, (7) defoliation, (8) wilting of leaves followed by death and (9) alteration of photosynthesis, transpiration and respiration.

Red clover (Trifolium pratense L.) is one of the most important of the true clovers. It has proved to be a very versatile species in its ability to adapt itself to a particular set of conditions, and a large number of races have been evolved within the species. Regional strains, which differ in productivity, winter hardiness, and disease resistance, have developed as a result of the selective action of local environmental conditions on this highly variable plant.

The elucidation of the nature of host pathogen relations is a problem of great theoretical and practical importance. One of the most promising lines of research for this problem seems to be in the field of physiological studies, in which the affects of infection on the metabolism of a host plant are studied. In most cases, metabolic studies which have been carried out on the nature of disease had to be performed on detached organs, detachment of which prevents the movement of materials in and/or out or the organ from taking place, i.e. prevents translocation.

Antimicrobial activity was discovered in the expressed and concentrated juices of buckwheat, and in the water soluble fractions of hot extracts using organic solvent(s). A phenolic chromogenic substance was found to be responsible for the antibiosis of the extracts. The degradatory products of the anthocyanin pigment from the plant were shown to have somewhat similar toxicities to those of the extracts. The organic acids, citric, malic and oxalic, reported present in appreciable quantities in the plant, were also assayed for antimicrobial properties, and were found to be somewhat more toxic than the phenolic substances. It was not possible to draw a definite relationship between the above antimicrobial properties, and the actual non-susceptibility of the plant to microbial attack.

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