1 91 2] GAGER— INGROWING SPROUTS 519 



through the cortex was digested by a substance secreted by the 

 emerging root. The same conclusion was reached later by Von 

 Hone (12) and by Van Tieghem (ii). Neither Reinke's nor 

 Van Tieghem's figures, however, show evidence of enzymatic 

 action. In 1896 Czapek (i) reported that he found in the excre- 

 tions of the roots of higher plants no evidence of any enzymes. 

 If they are present, the amounts are too small to be detected. 

 Pfeffer has declared for a mechanical modus operandi, aided by 

 some activity on the part of the cortical tissue. 



In 1894 Peirce (6) found that the roots of Vicia and Pisum 

 penetrated living tissue by mechanical pressure, unaided by 

 enzymes. He also states that the radicle of Pisum could enter 

 through the uninjured periderm of a potato from the outside. In 

 1903 Olufsen (5) reported a confirmation of Peirce's results, 

 but Pond (8) was unable to confirm them, and reported negative 

 results also for Vicia Faba and Lupinus albus. When the periderm 

 was wounded, the radicles of these seedlings entered easily and 

 penetrated the parenchymatous tissue. When the periderm was 

 unwounded, the radicles deeply indented the surface, but never 

 pierced through. Microscopic examination showed that the peri- 

 derm cells, and, to a less degree, the hypodermal cells also, were 

 compressed, but there was no evidence of corrosion. "The advan- 

 cing root formed callus, but when the periderm is wounded the 

 callus does not form " 



In one of Pond's experiments a potato tuber was cut in two and 



surfaces placed together and held firmly in this position 

 Then a channel was made in one half to within a few 



The 



by string. Then a channel was 

 millimeters of the skin, and the 1 

 whole was then incased in gypsum. The radicles perforated the 

 periderm of the first half from the inside, and were thus brought 

 into contact with the outside of the periderm of the other half, 

 but this they failed to penetrate. From these observations Pond 

 concludes that the mechanical push is too weak to accomplish 

 penetration from without. "Microscopical examination of the 

 flesh of a potato showed no evidence of any digestive action/ 7 



similar manner Pond 



Lup 



