228 PHYTOHORMONES 



be removed, the petiole subsequently falls off; but if urine 

 or auxin paste be applied to the petiole it remains in position 

 for a much longer time (Laibach, 1933a; Uhrova, 1934; 

 La Rue, 1935). AppHcation of large amounts of indole- 

 acetic, indole-butyric, or other related acids to the soil, 

 3 to 5 weeks before flowering was due, has been reported 

 to hasten the formation of flower buds in Turkish tobacco 

 (Hitchcock and Zimmerman, 1935). A hastening of flower- 

 ing has been found to be produced in various plants by 

 application to the soil of female sex hormones (see XIV B). 

 Hastening of flowering has also been recorded in peas and 

 beans as resulting from application of yeast extract (Virtanen 

 and Hansen, 1933, 1934). Little can be said about the mech- 

 anism of such phenomena pending more careful study. 



Interesting, particularly from a historical standpoint, 

 is the role which is apparently played by auxin in the phe- 

 nomena of post-floration of some orchids. It was shown 

 by Fitting in 1910 that the falling off of the flower and swell- 

 ing of the gynostemium of some tropical orchids after 

 flowering were brought about by the presence of the pollen 

 grains, and could also be caused by water extracts of the 

 pollinia (see II E) . The action was ascribed to a hormone 

 in the pollen, and this was the first use of the term hormone 

 in connection with plants. It was shown by Laibach (1932a) 

 that this substance is extractable with ether, behaving like 

 an acid in the extraction, and further that the extracts were 

 active on Avena. Hibiscus pollen gave similar results. Lai- 

 bach and Maschmann (1933) subsequently showed that 

 ether extracts of urine and animal tissue behaved in the 

 same way, and that action on the orchid gynostemium was 

 parallel with auxin action on Avena, all extracts which 

 had the one action having the other. The activity on the 

 orchid was destroyed by H2O0. The sweUing was entirely 

 due to cell enlargement. It was thus deduced that the effect 

 is due to the auxin in the pollinia, so that Fitting's '^Pol- 

 lenhormon," which may fairly be called the first plant 

 hormone, is identical with auxin. Experiments have not 



