116 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1939 



CULTIVATION OF EXCISED PLANT ORGANS 



Excised plant organs grown in culture offer very promising ma- 

 terial for many kinds of physiological problems. The growth of 

 excised roots of white moonflower has been found to be very markedly 

 enhanced by illumination. These roots cultured in light also develop 

 chlorophyll, and it has been found that they are capable of synthesiz- 

 ing vitamin C in light but not in darkness. This study, under- 

 taken by Dr. Weintraub in collaboration with Dr. M. E. Reid, of 

 the National Institute of Health, suggests that the vitamin C cus- 

 tomarily found in the colorless roots of intact plants is synthesized 

 in the shoots and thence transported to the roots. It is intended 

 to continue the study with excised roots incapable of synthesizing 

 chlorophyll. 



A study of the growth of excised leaves has also been initiated and 

 investigation of the influence of a number of growth factors is under 

 way. 



PLANT HOEMONES 



The assay method for growth-promoting substances, to which ref- 

 erence was made in last year's report, has been published. The next 

 step in this project, which is being carried on by Dr. Weintraub, 

 namely, the development of a quantitative technique for the isolation 

 of the hormones from the plant, has been undertaken, but is not yet 

 completed. With the use of these methods it is hoped to examine 

 the occurrence of the hormones in the plant as correlated with the 

 growth and curvature under the influence of light of various in- 

 tensities and wave lengths. In connection with the study of the 

 growth-substance extraction, some experiments have been made to 

 ascertain the identity of the naturally occurring hormone in the 

 oat plant. From the results thus far obtained, it appears that the 

 conclusion of other workers that the native hormone is auxin a, is 

 not necessarily valid. 



The volume of detailed work necessarily connected with these plant 

 growth studies could not have been done in the time these studies 

 have been in progress had it not been for the able assistance of 

 Messrs. Brydon and Zipf. 



STIMULATIVE ACTION OF ULTRAVIOLET RADIATION 



Dr. Meier has continued her studies on the stimulative action of 

 ultraviolet light. In this research she has shown that a stimula- 

 tive action causing increased cell multiplication of the green alga 

 Stichococcus hacillans Naeg. results from sublethal exposures to the 

 four short wave lengths of the ultraviolet experimented with, namely, 

 2352, 2483, 2652, and 2967 A. The optimum stimulation point occurs 



