26 GROWTH HORMONES IN PLANTS 



then moistened with a sohition of 1 g. citric acid, 50 cc. alcohol, 

 and 50 cc. water. If necessary, they may be kept for a time in 

 the refrigerator and later applied unilaterally to decapitated 

 Avena coleoptiles (Fig. 10). 



5. DIFFUSION OF GROWTH SUBSTANCE INTO WATER. Another 



method of extraction has been described by Gorter (1932). 

 The pieces of plant, for example, coleoptile tips, are placed upon a 

 layer of sand which is soaked with water. After a time they are 

 removed, the water filtered off, and the sand washed repeatedly. 

 The filtrate and rinsing water are either evaporated in a vacuum 

 or extracted with ether. The residue from the evaporated ether 



w) Iw ^ 



Fig. 10. — Curvatures of decapitated Avena coleoptiles resulting from applica- 

 tion of agar blocks upon which root tips of Vicia Faba had been standing for 

 4 hours. (From Boysen Jensen, 1933.) 



extract is dissolved in water which contains 160 mg. potassium 

 chloride and 0.2 cc. glacial acetic acid per liter; agar blocks are 

 placed in the solution, and later these are tested for growth sub- 

 stance in the usual way. 



6. EXTRACTION OF GROWTH SUBSTANCE WITH ALCOHOL. 



Growth substance can be extracted also from plant parts with 

 alcohol. The alcohol which is poured off is concentrated in a 

 vacuum, and the residue dissolved in an optional amount of 

 water; this solution is investigated either directly after mixing 

 with agar or after it has been purified with ether (the latter is 

 described later). 



7. EXTRACTION OF GROWTH SUBSTANCE WITH CHLOROFORM. 



Thimann (1934) has described a method of chloroform extraction 

 of growth substance from tissues. It consists, in brief, of killing 

 the fresh material by immersing it in a small amount of chloro- 

 form, adding 0.1 A'^ hydrochloric acid to the extent of about one- 

 fifth the volume of the chloroform, and grinding the mixture 

 thoroughly. The extract containing the growth substance is 



