194 PHYTOHORMONES 



its intensity would indicate but the effects of the other 

 Hghts are more or less proportional to their intensity. The 

 white columns thus represent the effect of light on the 

 effectiveness of the auxin in producing roots, while the shaded 

 columns represent a combination of this with the action of 

 light on auxin synthesis. The importance of light for the 

 synthesis of auxin in green parts has been discussed in IV ^4. 

 These experiments throw some light on the conflicting re- 

 sults mentioned above; in cuttings with an auxin storage 

 (deciduous plants in fall and winter, cj. XI G), root forma- 

 tion will be best in darkness. In leafy cuttings without auxin 

 storage, however, light will be required for auxin formation 

 and therefore for rooting. 



E. Effects of Factors Other than Auxin 



Carbohydrate. The production of roots (or any other 

 growth) by an etiolated cutting, deprived of the food reserves 

 in its seed, requires carbohydrate. This was clearly shown 

 by Bouillenne and Went (1933) with Impatiens; in one ex- 

 periment they record, after 10 days in 1.5 per cent dextrose, 

 an average of 7.25 roots per cutting, as against an average 

 of only 1.0 in water. Sucrose behaved similarly. Leaving 

 the cotyledons on, however, raised the average number to 

 15, which we can now explain as due to the combined effects 

 of sugar and auxin, both coming from the cotyledons (c/. 

 the analysis of the growth of hypocotyls in VD). In other 

 etiolated material the same is true; cuttings of etiolated 

 peas, for instance, gave 25 roots per 10 plants in 2 per cent 

 sucrose, and only 9 when in water. The sugar must be ap- 

 plied very soon after the auxin treatment; if the plants are 

 first placed in water for 2 days and then in sugar practically 

 no roots are formed {u). 



The kind of sugar used is of considerable importance; 

 sucrose and fructose give larger numbers of roots than dex- 

 trose under comparable conditions. The sugar also exerts 

 an effect on the length of the roots produced, fructose giving 

 the longest, and dextrose the shortest. Sucrose which has 



