Crystalline abscisin II, with a tentative molecular formula of C(15)H(20)O(4), has been isolated from young cotton fruit. It accelerates abscission when applied in amounts as low as 0.01 microg per abscission zone. It inhibits indoleacetic acid-induced straight growth of Avena coleoptiles but has no gibberellin activity on dwarf maize.

Slatis has raised a single valid point. The chromosome-per-cell distributions displayed in our put numbers on our observations. We do recognize the implications of such damage in our experimental cell populations, if the observations were significantly elevated above control values. We cannot say that they were, or that they were not.We feel that Slatis' attempt to show chromosome damage by pointing to differences which are the result of random sampling error is not a matter of a one-tailed or a two-tailed test.We agree that the pertinent statistical tests, at least for data in our Table 2, should be one-tailed. In fact, our conclusions were based on one-tailed ttests, the full results of which were not tabulated. The confidence limits given with our data were for the convenience of readers who wished to inform themselves of the magnitude of random sampling errors associated with the percentages in the Abscisic Acid: A New Name for Abscisin II (Dormin) Abscisin II was the name given to the second of two abscission-accelerating substances isolated (1) from cotton fruit. The same substance was subsequently isolated (2) from sycamore leaves as the result of a search for a "dormin" [an endogenous substance inducing dormancy (3)]. Since then, the substance has been identified in a large number of higher plants. The structure of abscisin II has been determined and confirmed by synthesis (4); structure and correct absolute configuration (5) are shown by the insert.

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