CHAPTER XI 



ROOT FORMATION 

 A. Root Formation as a Correlation Phenomenon 



In Chapter II .4 it has been pointed out that our earUest 

 knowledge of correlation was mainly based upon root forma- 

 tion. Beginning with Duhamel and Sachs, various investi- 

 gators have explained root formation on cuttings by the 

 accumulation of special root-forming substances near the 

 basal cut surface. Beijerinck (1886) emphasized the im- 

 portance of the leaves for root formation, although he was 

 apparently thinking rather of a nutritional effect. Vochting 

 (cf. VI B) studied both root formation and root develop- 

 ment, but with particular reference to polarity, the forma- 

 tion of the roots being considered rather as an indicator of 

 polarity than as a problem in itself. Among the factors in- 

 vestigated, Vochting stressed the importance of water, the 

 inhibiting effect of hght, and the tendency of gra\'ity to 

 induce root formation on the lower side of a horizontal 

 cutting. 



Of the other investigations of the various factors con- 

 trolling rooting, only the more relevant need be mentioned. 

 In the first place numerous attempts, largely unsuccessful, 

 have been made to correlate root formation or root gro\\i;h 

 with nutritive factors, especially with the carbohydrate: 

 nitrogen ratio (see for instance Goebel, 1902-1903; Reid, 

 1924; Carlson, 1929). However, it was emphasized by i\Iac- 

 Callum (1905) that nutrient conditions are not the principal 

 factors governing root formation. Morgan (1906) has shown 

 the same thing for regeneration in animals; the rate of 

 formation of new legs, after the removal of the original legs, 

 was found, in Salamanders and other animals, to be the 

 same when they were well-fed as when they were starved. 

 In this connection Kupfer (1907) made the interesting 



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