MORPHOLOGICAL AND HISTOLOGICAL MODIFICATIONS OF PINE SEEDLINGS INDUCED BY PETROLEUM NAPHTHA

Abstract

Pinus caribaea, P. sylvestris, and P. resinosa seedlings at various stages of growth were subjected to pre-emergence and postemergence treatments with Standard Weed Killer, a Stoddard solvent naphtha, at the rate of 50 to 1000 gal. per ac. Structural responses were a darkening and wilting of the cotyledons and hypocotyl in young seedlings and a yellowing and burning of the older foliage. Outstanding histological modifications were plasmolysis and cytolysis of the cortex, pith, and mesophyll and stomatal closure. Anatomical variation in pine seedlings is suggested as an explanation for species and organ differences in response to the petroleum spray. Less mature seedlings were more susceptible to the Stoddard solvent than older seedlings. Penetration, once the initial stages had been passed, was rapid, though limited in mature tissues by the thick-walled endodermis. The oil passed through the stomata and moved into the intercellular spaces. Once in the cell, the oil combined with the cell contents causing plasmolysis followed by cytolysis.