Page:Report of the Puerto Rico Experiment Station (IA CAT31294391015).pdf/14

 schooner to the experiment station at St. Croix, U. S. Virgin Islands, and were out of the ground about a week.

During this process the plants were handled at least six times. Balled plants gave the highest percentage of survival (55 percent) if the leaves or top were removed. Even if a few top leaves were left on the plants' survival was reduced considerably. Trees transported with bare root stock survived surprisingly well (46 percent) considering the rough treatment they received. Dipping the roots in lanolin, glycerine, or mud suspension was of no apparent value. Although higher percentages of survival were obtained with topped or defoliated balled trees, the cost of digging and transporting was considerably greater. Balled trees weighed from 25 to 40 pounds each, but topped, bare root trees wrapped in coco peat weighed only about one -tenth as much. The time required to dig the latter was about one-sixth that of the balled trees.

E. P. Hume

A previous mango air-layering experiment, using plant hormones mixed with expanded mica, gave good initial rooting. However, the media remained quite dry during the rooting period. Another experiment was conducted using coco peat treated with various concentrations of indolebutyric acid in place of expanded mica. The coco peat layers were wrapped with pliofilm to prevent drying out as in the earlier experiment. After 90 days, during which 20 inches of rain fell chiefly in the form of heavy showers, the girdled branches were cut and examined. The coco peat had a much higher moisture content than at the start of the experiment and, as a result, a number of the roots had turned black. The living bark, especially at the lower hormone concentrations, had developed considerable proliferation of the lenticels. Rooting in general was poorer than in the previous experiment, using expanded mica and conducted during the dry season. The highest concentration, 1,000 p. p. m., was toxic, killing both phloem and outer xylem in some cases. Roots 2 inches or more in length were found only in the 100- and 400-p. p. m. treatments.

A. J. Loustalot and E. P. Hume

The insertion of toothpicks impregnated with 4 mg. of indolebutyric acid in the stem of mangosteen, Garcinia mangostana L., seedlings, 1 inch above the crown, resulted in abnormal proliferation of roots in the treated area but top growth was reduced. It was expected that the treated plants might grow more rapidly during the second year because of the greater root system. Top growth measurement taken at the end of 2 years failed to show significantly greater growth by the treated plants. The treated plants had an abundance of new roots which were soft and more succulent than those on untreated plants. Many of them were destroyed as a result of attacks by insects and diseases. Thus, while the hormone treatment stimulated root development it actually operated to the disadvantage of the plant growth in general. The root hormone treatment as applied in this experiment was too strong because it overstimulated root formation at the expense of top growth.