Stimulation of Root Growth in Cuttings 97 



recognized for some time. Sorauer (1895) lays strong emphasis on the 

 need of aeration, especially for herbaceous cuttings. 



Kiister (1903) states that cuttings always callus more readily in a moist 

 atmosphere than in water, tho he considers transpiration, as well as 

 oxygen supply, a determining factor. 



Klebs (1903) found that cuttings of Salix pentandra develop roots only 

 at the cut end of the twig, not thruout its length as do cuttings of Salix 

 alba vitellina pendula (Spath.) ; however, if the cork layer is removed at 

 a point some distance from the cut end, roots will develop in or near this 

 region. He explains this on the theory that water is the determining 

 factor. He suggests that on removal of the impervious cork layer, water 

 enters the twig, and the roots then develop. He does not reaUze, ap- 

 parently, that when the twig is immersed the tissues must be practically 

 saturated — certaialy of greater water content than those of the basal 

 end when the cutting is suspended in moist air, yet under the latter con- 

 dition roots wUl develop freely. The more probable explanation is that 

 the removal of the cork allows for better aeration, thus increasing the 

 oxygen supply at that point as weU as supplying an outlet for the carbon 

 dioxide produced in respiration. The work of Appleman (1916) is sug- 

 gestive in this connection. He found that tubers of Solanum tuberosum 

 were caused to sprout when the skins were removed. The results he 

 explains as due to increased permeability to oxygen. 



It is very generally known that when potassium permanganate comes 

 in contact with organic matter, manganese dioxide is precipitated and 

 oxygen is liberated. Some of the most recent work on this line is that of 

 Bunzell and Hasselbring (1917), who found that various organic com- 

 pounds — • glucose, alcohol, and others — will decompose potassium 

 permanganate with the formation of manganese dioxide and in some cases 

 a straw-colored solution containing manganese and giving strong oxidase 

 reactions. 



The cuttings treated with potassium permanganate were very much 

 blackened by this precipitate of oxide of manganese, which clings firmly 

 to the surface of the twig. Sections of the twig showed the oxide de- 

 posited |in the xylem cells for a distance of from one to four millimeters 

 from the cut end. They showed also a sUght penetration into the cortex 

 cells thruout the length of the immersed part. 



