Chemistry and Qrowth 



These two vitamins, according to Borgstrom, really acceler- 

 ate growth of roots, and therefore are growth-promoting, in 

 the sense used in this book. 



Further evidence of a favourable action of vitamin B^ has 

 been provided by Bonner and Greene (1938, E) whose con- 

 clusions are interesting (see p. 68). 



It may be suggested here that the glycerides of acids active 

 as growth-regulators might be safe vehicles of application. 

 They resemble the true fats in being non-volatile and in 

 being practically insoluble in water, but can hydrolyze slowly. 

 Methods of preparation of some lower phenyl glycerides are 

 given by Darzens (1937). 



Plant-Growth Substances i?i Tissue Culture 



Some very interesting work has been briefly reported by 

 LaRue (1935). He cultivated minute pieces of the hypocotyl 

 (first shoot) of dandelion, wild lettuce, and ox-eye daisy. A 

 mineral culture solution was used, one lot receiving indole- 

 acetic acid in the very high dilution of one part in 20,000,000. 

 Successful growth took place only in the culture receiving the 

 indole-acetic acid. The resulting plants developed numerous 

 leaves and extensive root systems, and were believed by 

 LaRue to be the first successful tissue cultures in which com- 

 plete plants had been grown. See also the paper of Gautheret 

 (1937), who found that indole-acetic acid in appropriate con- 

 centration was favourable to the growth of cambial tissue of 

 willow. 



Kaufmann (1938) removed the cotyledons of seeds, let the 

 seeds swell for two days in water, then placed them in the 

 dark in media containing potassium salts, sugar (sucrose),^ 

 and indole-acetic acid. A 24-hour treatment with concentra- 

 tions of one-millionth and one-hundred thousand millionth 

 per cent, of growth-substance induced maximal growth of 

 root. 



Indole-acetic acid added to nutrient agar in which excised 



^This obligatory use of sugar in cultivation of excised roots, for which 

 it replaces the normal photosynthetized sugar of whole plants, should not be 

 confused with the use of sugar mentioned on pages 43 and 44. For other work 

 on excised roots see p. 115. 



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