EMBRYO DEVELOPMENT IN FOUR DATURA SPECIES FOLLOWING SELF AND HYBRID POLLINATIONS

Abstract

Englislh plantain is a long-day plant developing flowers when exposed to 15 or more long days or to 9 or more days of continuous illumination. Plants have been kept for over 14 months in the vegetative condition by continuous exposure to short-day conditions. Plantain will develop flowers when exposed to 25 long days even though this treatment is not continuous but is interrupted by 10 or 20 consecutive short days. The changes which occur during partial photoperiodic induction apparently persist during relatively long periods of exposure to light and dark periods whose lengths are not favorable for flowering. Plantain exposed to photoperiodic cycles (other than of 24 hr. duration) flowered when exposed to cycles consisting of short light (14 hr. or less) and short dark periods (10 hr. or less), long light and short dark periods, and long light and long dark periods; but remained vegetative when exposed to cycles consisting of short light and long dark periods. It is suggested that in the development of floral structures of this long-day plant, there may be two reactions which occur during exposure to light. The first reaction is unstable and is destroyed during darkness, while the second is relatively permanent and when established will persist during long periods unfavorable to the stimulation of flowering. It is further suggested that the second reaction occurs after the primarv reaction has reached a threshold value, and upon reaching sufficient intensity results in floral development.