THE REDUCTION OF THE GROWTH AND WEIGHT OF PLANTS BY A 2ND AND LATER GENERATIONS OF NEMATODES

Relative weights of 97 days-old oat plants in pots inoculated with a r ange of densities of Heterodera avenae eggs and juveniles at sowing as well as once or twice on later dates, were the products of the relati ve weights that would have been obtained after single inoculations on the same dates. Plants in pots inoculated with large nematode densitie s at sowing were an exception. Their physiological age at the time of the later inoculations was reduced (retardation of development), which made them more sensitive to weight reduction by the nematodes than un inoculated plants of the same actual age. The plants were less toleran t to nematodes already present at sowing than to those introduced into the soil later but which attacked the same roots at the same time. Th is creates a theoretical paradox.