70 GROWTH HORMONES IN PLANTS 



demonstrated also in higher animal tissues, both normal and 

 pathological, in saliva and in crustaceans, etc. 



The question of growth-substance formation is of very great 

 importance. There is some indication that the plant-growth 

 hormones found in animals may have their origin in the materials 

 supplied in plant foods. The action of the enzyme lipase upon 

 peanut oil is known to result in the production of growth hor- 

 mone. Diets rich in fats increase the auxin content of urine. 



The formation of growth substances in molds and bacteria has 

 been studied in relation to the character of the nutrient sub- 

 stratum; the following substances in the medium were favorable 

 for growth-substance formation: glucose peptone, glucose- 

 ammonium tartrate, and tryptophane, tyrosin and several other 

 amino acids. 



It has been learned recently that the growth substances stored 

 in seeds of higher plants are of great significance in germination 

 and seedling growth. The amount of growth substance in seeds 

 is increased upon hydration of the stored foods during germina- 

 tion. Light seems to promote its formation in seedlings and in 

 the growing parts of young leaves, perhaps also in meristems. 

 Localized chemical changes in plants, e.g., increased acidity, may 

 release active growth hormone from the inactive salt form. 

 Ethylene treatment apparently decreases the production of 

 growth substance in Vicia and Avena. Within limits, higher 

 temperatures have been found to result in increased production of 

 the substances both in lower plants (molds) and in the roots of 

 higher plants. Li view of the limited information existing at 

 present on this important subject, an extremely promising field is 

 open for further investigation. 



