REST IN BUDS OF WOODY PLANTS 



207 



XL XK I 



Date of sampling 



H Nil 

 \ 



Fig. 1. Inhibitory activity in neutral fraction of ether extracts from grape 

 buds of two Vitis crosses. Expressed as positive curvature of the coleoptile 



of Avena after SpiegeU^. = V. vinifera / V. berlandieri; 



= V. vinifera , : V. rupestris 



in Spring, about 70 days before the V. berlandieri cross. Since 

 these investigations were pubHshed, similar resuhs have been 

 obtained with a number of woody plants, maximum inhibitor 

 concentration always being found during 'mid rest'. On the 

 other hand, with most plants growth-promoter activity is 

 gradually reduced during entry into rest, disappearing entirely 

 in some species during 'mid rest' and reappearing again towards 

 the end of the rest period. 



Considering growth-promoting substances, the activity of 

 indoleacetic acid would seem to be very pronounced in most 

 plants; indeed Spiegel considered it to be the only promoter in 

 grape vine. In many plants indolethylacetate and indolepyruvic 

 acid play an important part. Furthermore, the Rf values of a 

 few unknown growth-promoters have been reported. As regards 

 inhibitors, two substances have lately been identified, but there 

 would seem to exist quite a number of additional ones. In buds 

 of peach trees Hendershott and Walker^^ identified naringenin 

 (trihydroxyflavanone) and Housley and Taylor^' revealed the 

 mixture of substances making up Bennett-Clark's beta inhibitor, 



References p. 208 



