Abstract
1. It has been confirmed that the spore formation of Pythium ultimum is greatly promoted by some organic substance contained in corn or in carrot.
2. This substance can not be replaced by the known growth substances such as water-soluble vitamins, amino acids, bases of nucleic acids or minor-elements.
3. This substance is very unstable and can be easily inactivated by illumination or by oxidation or by alkali treatment.
