ULTRAVIOLET LIGHT AND THE DEVELOPMENT OF FUCUS EGGS AS AFFECTED BY AUXIN AND pH

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Abstract
Unilateral irradiation of Fucus eggs by suitable moderate doses of u.-v. (2537 A) causes rhizoids to form on the non-irradiated halves of the eggs. The response of populations of eggs is proportional, over a wide range, to the logarithm of the dosage. When moderate doses of unilateral u.-v. are followed by prolonged exposures to the directive effect of white light from the opposite sides of the eggs, the rhizoids form on the surfaces that were irradiated with u.-v. Therefore, the u.-v. does not determine the position of rhizoid formation merely by causing extensive, general damage and incapacita-tion of the surface upon which it falls. B-indole acetic acid has very little effect on the sensitivity of the eggs to the polarity determining action of u.-v. It does not revive eggs that have been so strongly irradiated that rhizoid formation and cell division are retarded or inhibited. Therefore, the u.-v. does not appear to act on the eggs primarily by affecting or destroying auxin (B-indole acetic acid). The sensitivity of the eggs to the polarity determining effect of moderate dosages of 2537 A is considerably increased if the medium is acidified from pH 8 to pH 6. The sensitivity to the inhibitory effects of strong dosages is considerably decreased at pH 6. The 2 phenomena thus appear to depend on different actions of the u.-v.