SOME HISTOLOGTCAL EFFECTS OF DIRECT CONTACT OF PINUS RESINOSA SEEDS AND YOUNG SEEDLINGS WITH 2,4,5‐T*

Abstract

Summary. Direct contact of seeds and recently emerged seedlings with 2,4,5‐T at 25 or 100 ppm caused abnormal development of Pinus resinosa Ait. seedlings. The first observed effect of 2,4,5‐T treatment at 25 ppm was cessation of cell division and expansion in the roots. Subsequently the herbicide stimulated proliferation and expansion of parenchyma ceils in the stem and cotyledons, causing abnormal thickening of the seedlings. Parenchyma cells in the upper stem became disorganized and many of them collapsed. Callus tissue then formed in the region of tissue disintegration. The herbicide also inhibited formation of primary needle primordia and expansion of primary needles. In treated plants the cotyledons were fused to primary needles. Cell proliferation and formation of callus tissue were greater with 2,4,5‐T at 100 ppm than at 25 ppm. Quelques effets histologiques du contact direct des semences et desjeunes plantules de Pintis resinosa avec le 2,4,5‐T