1. Irradiation of soaked seeds of Helianthus annuus causes a slight decrease in percentage of germination. The average total growth of the plants is less, and the average time of blossoming is shortened, even with doses so light that there are no immediate visible effects. A checking effect, proportional to the doses, is evident during the first three weeks of growth after seeds have been irradiated with medium doses. On unfolding, the leaves present a peculiar pitted or mosaic appearance, which seems to be due to an unequal distribution of chlorophyll, when medium or heavy doses are given the seeds. Heavy dosage does not stop development of soaked seeds until the cotyledons have been partially or wholly pushed through the soil. The root tip becomes brown in color and no growing stem tip appears. 2. Fasciations of stems, leaves, and flowers are induced by irradiation of seeds and seedlings with medium doses. Stem fasciations commonly took the form of flattening and dichotomous splitting of the main stem, ...