HORMONES 213 



certain very complicated physiological processes otherwise 

 inexplicable. 



Of recent years the study of the transmission of stimuli, 

 in relation to correlation of growth and development,* geo- 

 tropism and heliotropism, by the movements of hormones, 

 has resulted in the publication of a large number of obser- 

 vations a consideration of which is hardly possible without an 

 account of the phenomena associated with irritability, a big 

 subject outside the scope of a treatise on the metabolic pro- 

 cesses of plants. 



* See Haberlandt : " Sitz. Preuss. Akad. Wiss.," 1921, 695. 861; 

 " Beitr. Allegm. Bot.," 1923, 2, 1. Gilbert: " Bot. Gaz.," 1926, 81, I. 

 Reed : " journ. Agric. Res.," 1921, 21, 849. Snow : " Ann. Bot.," 1923. 

 37, 43; 1924, 38, 163, 841. Soding: " Jahrb. Wiss. Bot.," 1925. 64, 587. 

 Suebert : " Zeit. Bot.," 1925, 17, 49. Tschirch : " Vierteljahr. Natur. Ges ; 

 Zurich," 1921, 66, 201. Went : " Kon. Akad. Wetens. Amsterdam," 

 1926. 30, 1. 



