60 GROWTH HORMONES IN PLANTS 



in these plants has been made by the Avena test. Using agar 

 blocks, Soding (19326) extracted growth substance from Heliopsis 

 laevis and Ornithogalum but was unsuccessful with Cephalaria 

 tatarica, as with Symphoricarpos and Rheum mentioned above. 

 It was possible to obtain positive tests in the latter, however, by 

 testing with agar blocks applied to seedlings of the same species 

 (Soding, 19356), Fliry (1932) extracted growth substance from 

 the Helianthus plumule (see also Beyer, 1925). Tests for 

 growth hormones in Tradescantia (Uyldert, 1931) and in beech, 

 oak, and pine (Huber, 1931) gave negative results. Czaja 

 (1934) later showed that growth substance is present in the burst- 

 ing buds of various woody plants {Aesculus hippocastanum and 

 several others). 



Van Overbeek (1933) and Dijkman (1934) have published 

 extensive investigations on the occurrence of growth substance 

 in seedlings of Raphanus and Lupinus. In Raphanus it is 

 formed by the cotyledons from which it can be extracted ; if the 

 cotyledons are removed, the hypocotyl tip then assumes the 

 function of formation. The situation is somewhat different in 

 Lupinus (Dijkman, 1934) and Vicia Faba (van der Laan, 1934). 

 In these plants, there appears to be no center of production; 

 growth substance is present in all growing regions. It is probably 

 distributed more or less equally throughout the Phaseolus seed- 

 ling (unpublished work of Boysen Jensen). Thimann and 

 Skoog (1934) found that the terminal bud of Vicia Faba produces 

 it, as do also the lateral buds during active growth. 



Laibach and Meyer (1935) have demonstrated that the amount 

 of growth substance occurring in Helianthus varies according to 

 the stage of development ; it is abundant during seed germination 

 and early growth, relatively scarce during the period of vigorous 

 vegetative activity, and high again as the plant comes into fruit 

 (Fig. 19). The tests were made by taking 20 g. of fresh material 

 from different parts of the plant at different stages of develop- 

 ment. Growth substance was extracted from this material by 

 boiling in a small amount of acidulated 96 per cent alcohol. 

 The concentrated extract was mixed with lanolin and applied 

 unilaterally to Avena coleoptiles. 



The investigations of Schmitz (1933) indicate that all the 

 growing regions of stems in many genera of grasses contain growth 

 substance. Although no growth substance was found in mature 



