122 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1947 



Evidence has been obtained, however, that dormancy and germina- 

 tion in this species is regulated, or at least influenced by an endo- 

 genous inhibitory substance. The nature of this inhibitor and the 

 mode of its action are being studied. 



A critical review of the literature dealing with germination of 

 lettuce is also in preparation. 



Effect of light on development of grass seedlings. Various phases 

 of this project have been carried forward as time permitted. A com- 

 parative investigation of the action spectrum for inhibition of meso- 

 cotyl growth in several species has been published. Tests on the 

 influence of several seed-disinfection treatments on subsequent seed- 

 ling development have been completed. Additional experiments have 

 been made on the effects of various salts on growth of etiolated oats. 

 In order to explain the observed gross morphological effects of light 

 and other environmental factors on mesocotyl elongation, a histologi- 

 cal study of this organ is in progress. A large number of slides have 

 been prepared and are being examined. It is planned to resume the 

 experiments on the interrelation between light and temperature as 

 affecting coleoptile and root growth as soon as the necessary equip- 

 ment, now being constructed, is available. 



Volatile plant-growth inhibitors. It was observed that in a wooden 

 growth chamber, of which the interior had been varnished, the germi- 

 nation of several species of seeds was completely checked or greatly 

 retarded, although all the commonly recognized environmental con- 

 ditions were favorable for development. On removal from this cham- 

 ber normal development was resumed promptly. As the plants were 

 not in direct contact with the original box it appeared that a volatile 

 substance of great physiological activity was present. A large 

 number of subsequent tests showed that volatile inhibitors are indeed 

 produced, presumably as the result of oxidation processes, by films of 

 varnishes, drying oils, unsaturated fat acids, and by several species of 

 wood. The rapid and complete reversibility of the inhibition is espe- 

 cially remarkable. An agent with these properties might conceivably 

 be of considerable value both in plant physiological experimentation 

 and in practical plant culture. Studies on the identity of the respon- 

 sible substance, or substances, are in progress. 



PUBLICATIONS 



The following publications relating to the work of the Observatory 

 were issued during the year : 



Abbot, C. G., 1946-47 report on tlie 27.0074-day cycle in Washington precipitation. 



Smithsonian Misc. Coll., vol. 107, No. 3, March 1947. 

 Abbot, O. G., The earth and the stars. D. Van Nostrand Co., Inc., New York. 



1946. 288 pp. 



