The Growth Substances Content of Germinating Lettuce Seeds.

The possibility of an excess of IAA as being the germination preventing mechanism of light sensitive lettuce seeds was investigated. No IAA was found in the dry seeds. Growth promoting substances appear in seedlings, only when germination proceeds. Two acidic growth inhibiting substances were the only growth active substances present in the dry seeds. These substances apparently disappear when germination proceeds. A variety of other active substances appears during germination. The chemical nature of the growth inhibiting substances in the dry seeds, also the reaction of these substances to light are still not known. After this paper had been submitted to the press, a paper by Wareing P. E. and Foda V. entitled "Possible Role of Growth Inhibitors in the Dormancy of Xanthium and Lettuce". Nature (in press) was brought to our notice. The behaviour of the growth inhibitors found by these authors is similar to those found by us. The inhibitors are probably not identical due to differences in isolation procedure. Further investigations by one of us (S. GB) have shown that some of the acid substances extracted from lettuce seeds inhibit their germination. [ABSTRACT FROM AUTHOR]