Walter H. Muller

A comparison of the relative naturalization ability of two Schinus species in southern California. I. Seed germination.

NILSEN, E. T., and W. H. MULLER (Dept. Biol. Sci., Univ. of Calif., Santa Barbara, CA 93106). A comparison of the relative naturalization ability of two Schinus species in southern California. I: Seed germination. Bull. Torrey Bot. Club 107: 51-56. 1980.-Two South American pepper trees, Schinus molle L. and Schinus terebinthifolius Raddi, have been grown in Santa Barbara as ornamentals for at least 100 years. Yet only S. molle L. has become naturalized, even though both taxa are vigorous colonizers. Seed germination characteristics were studied for both species to determine a possible mechanism which inhibits the naturalization of S. terebinthifolius Raddi in southern California. Several germination characteristics were found to differ between these two species, such as relative cold tolerance, acid treatment requirements, and the time between imbibition and germination. The slow germination rate of S. terebinthifolius Raddi may inhibit establishment by not allowing germination and root development during the brief periods of ample soil moisture in southern California. An endogenous germination inhibition system of phenolic acids is suggested for both species. Research is continuing on relative seedling establishment, and the endogenous inhibition system.

VOLATILE GROWTH INHIBITORS PRODUCED BY SALVIA LEUCOPHYLLA: EFFECTS ON SEEDLING ROOT TIP

A B S T RA C T Volatile monoterpenes emanating from leaves of Salvia leucophylla (Labiatae) are responsible for anatomical and physiological changes occurring in herb seedlings which were exposed to the vapors. Examination of treated root tip cells from Cucumis sativus by electron microscopy revealed widespread systemic disturbances. These included the accumulation of globules which appear to be lipid in nature in the cytoplasm, a drastic reduction in the number of a variety of intact organelles including mitochondria, and a disruption of membranes surrounding nuclei, mitochondria, and dictyosomes. These effects, coupled with the effects of environmental stress, may account for the failure of herb seedlings to survive in the areas adjacent to Salvia thickets.

A comparison of the relative naturalizing ability of two Schinus species (Anacardiaceae) in southern California. II: Seedling establishment.

NILSEN, E. T., and W. H. MULLER (Dept. Biol. Sci., Univ. California, Santa Barbara, CA 93106). A comparison of the relative naturalizing ability of two Schinus species (Anacardiaceae) in southern California. II: Seedling establishment. Bull. Torrey Bot. Club 107: 232-237. 1980.-During the last 100-200 years two South American taxa, Schinus molle and Schinus terebinthifolius, have been grown as shade trees in southern California. Although both species have potential naturalizing ability, only S. molle has become naturalized in southern California. Seedling establishment characteristics were compared for both species to ascertain a possible mechanism preventing the naturalization of S. terebinthifolius. Based on the root to leaf area ratios, plant moisture content at permanent wilting, the ability of the plant to extract water from the soil, and leaf density, S. terebinthif ?lius was better adapted to drought. This species had a faster growth rate than S. molle and it allocated a greater portion of its photosynthate to root development. On the other hand, S. molle allocated more photosynthate to leaves and stem growth. Growth of both species was equally inhibited by low light intensities. Results of these growth experiments indicated that S. terebinthifolius seedlings may have a greater ability to become established in the Mediterranean growing season of southern California, and a greater ability to withstand the drought of the following dry season. Therefore, the mechanism which prevents the naturalization of S. terebinthifolius is most likely associated with another aspect of the life cycle, probably seed germination.