Stimulation of Root Growth in Cuttings 111 



As shown also by other experiments, manganese sulfate, as well as 

 potassium permanganate, is more toxic when the twigs are placed in 

 sand than when they are placed in water. This is probably due to the 

 fact that when the twigs are rinsed and placed in water, the water further 

 dilutes the small quantity of salt that may be carried over; while when 

 the twigs are placed in sand, any such salt is not diluted but is perhaps 

 concentrated as a result of slight evaporation from the surface of the stem. 

 Weaker solutions of manganese sulfate, however, caused increased growth 

 in the three experiments in which they were used. 



DISCUSSION OF STIMULATION BY COMPOUNDS OTHER THAN POTASSIUM 



PERMANGANATE 



Tho the results are not conclusive in all cases, there are at least indica- 

 tions of root stimulation in cuttings treated with MnSOi, Mn02, FeCls, 

 Fe2(S04)3, AI2CI6, H3PO4, and H3BO3. The writer has found no refer- 

 ences in literature concerning the effect of inorganic compounds on the 

 root growth of cuttings. There are reported, however, a number of 

 instances showing that certain of the above-mentioned substances have 

 served to increase root growth in seedlings. A few of these are here 

 considered. 



Manganese 



Loew (1904-05) reports that marked stimulation of roots of radishes 

 resulted from the addition of manganese sulfate at the rate of 94 grams 

 per square meter of soil. The treatment had no effect on top growth. 

 Loew, as well as some of his Japanese students, reported several experi- 

 ments indicating stimulation by manganese compounds, but no other 

 mention is made of their effect on root growth. Furthermore, many of 

 the conclusions are not very reUable, as they are based on results obtained 

 with only a few individual plants with no dupUcation. 



Micheels and De Heen (1906) report that coUoidal suspensions of man- 

 ganese have a marked stimulating effect on the roots of germinating 

 wheat. Colloidal tin also has a stimulating effect on the roots of ger- 

 minating peas, buckwheat, oats, and wheat (Micheels and De Heen, 

 1905), but the stimulation is less marked than that obtained with man- 

 ganese (Micheels and De Heen, 1906). The seeds used in these experi- 

 ments were soaked for about twenty-four hours in the solutions _and were 



