[Eco-physiological studies on desert plants : VI. Germination and growth inhibitors in the fruits of Zilla spinosa Prantl].

1. The germination of Lepidium sativum seeds is inhibited by the water extract from pericarps of Zilla spinosa. This inhibitory effect is reversible. Irradiation of the extract with UV showed no influence on the inhibitory effects of the extract. On the other hand, boiling the extract (of high concentration) reduces the inhibitory effect to a great extent. The inhibition was found not to be due to the osmotic influence of the extract. 2. Similar inhibitory effects of the extract were obtained with the seeds of Zilla spinosa. 3. Using organic solvents it is possible to distinguish between promotors and inhibitors of germination and growth. The substances promoting the linear growth, specially of the root, and the dry matter production are separated by organic solvents. 4. Pericarp extracts of old fruits shed from the mother plant a long time ago have less inhibitory effect on germination. However, these extracts promote the linear growth of the seedlings. In other words, the growth promoting substance (or substances) are not affected by aging whereas the germination inhibitors are partly destroyed or removed. 5. The ecological importance of the presence of germination and growth inhibitors and promoters is discussed.