The apparatus for the Oostenbrink direct cottonwool filter extraction method was modified for more efficient use of laboratory space. Yields of Pratylenchus penetrans were larger than those of Xiphinema americanum by this method but the converse was true for the Cobb method.

Under aseptic conditions, Pratylenchus penetrans (Cobb, 1917) Filip. & Stek., 1941, was pathogenic to roots of strawberry seedlings. After penetrating the epidermis, the nematodes aligned themselves with the long axis of the root at various depths in the cortical parenchyma. Although the endodermis was not invaded by the nematode, it was the first tissue to become discolored. Later, a less intense discoloration was observed in the cortex and epidermis, with the formation of polyderm beneath the damaged endodermis. The intensity of discoloration may be associated with the concentration of phenolic substances in the different tissues.

Celery seedlings, g':rown aseptically in silica sa-nd with .plant nutrients' were in'oculated ,i'iih"surface-st6rilized specimens of the root lesion nematode Pratylenchus penetrans (Cobb, 1917) pitip. t Steb., 1941r The reactions of invaded rooti *"re sfudied microscopically' The epidermis, -cort-ex, and endodermis of young celery roots showed d-ifferent degrees of discoloration after invasion 6f P.ienetrans, with the endodermis mbst severely .affected.Pratylenchus peneffans'qlas a pnmary parasite and pathogen of celery.

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