THE EFFECT OF UNILATERAL ULTRAVIOLET LIGHT ON THE DEVELOPMENT OF THE FUCUS EGG

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Abstract
When Fucus eggs that have been fertilized for a sufficient length of time are irradiated unilaterally with monochromatic u.-v. (2804 A) of adequate intensity, 97-100% form rhizoids on the halves away from the source of radiation. The responsiveness of a population of eggs increases gradually after fertilization and does not reach a maximum until about 7 hrs. at 15[degree] C. This is still some hrs. before the earliest rhizoids form. The response of the eggs to 2804 A is pro-portional, over a wide range, to the logarithm of the dosage. Rhizoid formation may be inhibited by a sufficient dose of 2804 A without cytolysis. Other effective wavelengths are 3660, 3130, 2654, 2537, 2482 and 2345 A; 3660 and 3130 A are less effective. Fucus eggs absorb less 3660 than 2804 A, but the difference in effectiveness is greater than the difference in absorption.