Toxic Substances from the Culture Media of Guayule which may Inhibit Growth

Abstract

1. The experiments indicate that substances unfavorable to the growth of guayule plants emanate from the roots of actively growing plants of this species. These substances are organic in nature and can be extracted from nutrient solution which has previously been flushed through gravel cultures of guayule plants. 2. The growth-inhibitory extracts were assayed for their toxic activity by application to guayule seedlings grown in solution cultures under standard conditions. 3. The growth-inhibitory substances contained in nutrient solution which has been recirculated through guayule cultures are ether-soluble acidic compounds. They were not, however, isolated in pure form. 4. A potent source of growth-inhibitory substance was found in water in which guayule roots were allowed to soak briefly. From this water two compounds inhibitory to the growth of guayule plants were isolated in crystalline form: cinnamic acid, and a second unidentified organic acid.