Rooting 205 



were more readily utilized than inorganic forms in the promotion of 

 rooting. This is in agreement with previous reports that biotin (Went 

 and Thimann, 1937, p. 239) and adenine (Thimann and Poutasse, 

 1941) were the most promotive of a variety of nitrogenous materials 

 tested. Van Overbeek et al (1946) found that neither of these com- 

 pounds was as good as arginine. It is entirely possible that the most 

 effective organic form of soluble nitrogen varies from one species of 

 plant to another. 



Of course nutrient materials are of importance in rooting not only 

 in relation to their ratio with auxin, but also in terms of the amount 

 of substrate present for the actual growth of roots. It is not surprising 

 to find that many workers have correlated ease of rooting with the 

 carbohydrate reserve of a plant. When carbohydrate reserves are 

 abundant, rooting is greatly facilitated (Kraus and Kraybill, 1918; 

 Carlson, 1929). The relative level of soluble nitrogen materials in the 

 cutting also has a bearing on ease of rooting, and the optimum level 

 of these compounds is low in proportion to the carbohydrate level. 



I 2 



LEAVES PER CUTTING 



Fig. 88. The effects of leaves present on cuttings of red hibiscus upon some 

 carbohydrate and nitrogen constituents of the cuttings (van Overbeek et al, 1946). 



