igi2] GAGER— INGROWING SPROUTS 521 



found, and since the epidermal cells are more nearly isodiametric 

 in normal sprouts, it was expected that the chemical examination 

 would disclose the presence of enzymes. Such however was not 

 the case. No enzymes were detected, and this experience empha- 

 sizes the truth that any inference as to the function of an organ or 

 tissue, based upon structure alone, cannot always be relied upon, 

 unless substantiated by positive evidence. # 



Further confirmation of the absence of enzymatic action was 

 obtained by examining microscopic sections of the walls of the 

 channels made by the sprouts in the tissue of the tuber. There 

 were no signs of corrosion of the cell walls nor of the starch grains 

 within the cells (plate fig. 2). 



Only one alternative remained: the sprouts made their way 

 through the tissue of the tuber by mechanical pressure alone. 

 This conclusion found abundant confirmation. The wall cells of 

 the channels made by the sprouts were greatly compressed by the 

 advancing tip (plate figs. 2 and 4). In light of the studies 

 the mode of emergence of lateral roots, it is instructive to compare 



made 



plate figs. 3 and 4. This latter figure is a detail of the tissues at 

 the point marked C in plate fig. 1. Fortunately, at this point a 

 lateral root had begun to develop, and it is clearly seen (fig. 3), not 

 only that the walls of the cortical cells show no signs of enzymatic 

 action, but that they are evidently compressed by the advance of 

 the developing root tip. The paths of the ingrowing sprouts and 

 of emerging lateral roots are evidently made in the same manner ? 

 namely by mechanical pressure alone, unaided by enzymatic action. 



Experimental production of ingrowing sprouts 



But how did the ingrowing sprouts start ? Do they, as sug- 

 gested above, represent normal sprouts that for some unexplained 

 reason turned their tips toward the tuber and penetrated through 

 the skin? There is no evidence for this view. In numerous 

 cases where the "eyes" were deeply indented, small sprouts grew 

 out laterally until their tips came into contact with the skin of 

 the potato. But, as in the case of Pond's attempt to cause one 

 root of Lupinus to penetrate another held firmly at right angles 

 to it, so here the surface of the potato was indented by the tip 



