122 Otis F. Curtis 



Effect of sugar with manganese dioxide, boric acid, or ferric chloride 



Since the cuttings were injured when left continuously in sugar solutions, 

 it was thought possible that the toxicity might be reduced by the addition 

 of some compound which might either retard the growth of bacteria or 

 oxidize toxic compounds produced by them. For that reason the following 

 experiment was undertaken, in which manganese dioxide and boric acid 

 were added to the sugar solutions. On October 6 the twigs in the poorer 

 culture of each pair were rinsed and placed in fresh water. Final notes 

 were taken on December 16, and the results of the experiment appear in 

 table 16. 



As shown by table 16, the stronger solutions of sugar retarded or 

 inhibited root growth. The weakest solution, 0.1 per cent, however, 

 caused an increased development. The presence of manganese dioxide 

 resulted injuriously, either when used alone or when combined with 

 sugar. Boric acid, on the other hand, stimulated growth, as has pre- 

 viously been shown. It also partially overcame the inhibiting effect 

 resulting from the presence of sugar. 



The retardation of root growth in the presence of sugar is probably 

 due to the formation of some toxic compounds resulting from the action 

 of bacteria and fungi. In several of the cultures alcohol could be detected 

 both by its odor and by iodoform test. Unless the period is too long, 

 the inhibiting effect of sugar continues only as long as the twigs are left 

 in the solution; after being rinsed and placed in fresh water, as indicated 

 by the table, many twigs in which the root growth had formerly been 

 inhibited by the sugar developed normal roots, and judged from their 

 appearance some of these twigs had even greater root development than 

 had the checks. 



In another experiment, started on October 15, fully matured cuttings 

 of Ligustrum were allowed to stand continuously in sugar solutions alone, 

 and also in sugar to which was added ferric chloride, boric acid, or manga- 

 nese dioxide. In every case the presence of sugar varying from 0.04 to 

 0.0004 molecular strength, retarded root formation. The presence of the 

 inorganic compounds seemed even to increase the retarding effect of the 

 sugar. When potassium permanganate was present with the sugar, 

 however, the retarding effect of the latter was largely overcome. 



