520 BOTANICAL GAZETTE [December 



epidermis of another Lupinus radicle. The second radicle was 

 always deeply indented, but no signs appeared of corrosion of the 

 surface. If the surface was even very slightly wounded, as for 

 example by pricking it with a fine glass point, then the other 

 radicle easily entered and passed entirely through without callus 

 formation. The penetrating root, however, was never found to 

 pass through the central cylinder, but always around it, thus indi- 

 cating more resistance than that offered by the cortex. The cylin- 

 der was indented, but there was no evidence of corrosion of its cells. 

 Starch grains did not appear digested either by autolysis or by the 

 entered root. The results of mechanically forcing a glass rod into 

 the tissue could not be distinguished from those produced by an 

 entering radicle. The conclusion drawn was that the mechanical 

 push was not sufficient to pierce the cuticle from the outside, and 

 that "if the radicle or the lateral root secretes an enzyme, such 

 enzyme has no digestive action upon the cuticle." 



As in the case of the roots, so with the potato, the course of 

 procedure for a solution of the problem is clearly indicated. If the 

 channels were the result of enzymatic action we would expect to 

 find, first, in the tips of the sprouts an enzyme able to digest the 

 potato tissue; second, evidence of enzymatic action in the tissue 

 itself; third, absence of any evidence of mechanical pressure; and 

 finally, we might expect to find the epidermis of the ingrowing 

 sprout modified in the direction of glandular epithelium. If the 

 sprout merely pushed its way through the tissue of the tuber, we 

 would find no signs of enzymes or of enzymatic action, but rather 

 positive indication of mechanical pressure. 



Physiological and anatomical study 





A considerable quantity of tips of the ingrowing sprouts was 

 given to Professor William J. Gies, of Columbia University, who 

 kindly offered to have them tested for enzymes. While waiting 

 for a report on this test, microscopic sections of the sprouts were 

 examined, to see if there was any modification of the epidermis in 

 the direction of a glandular epithelium, such for example as that 

 on the scutellum of the embryo of Zea Mays. As is clearly shown 

 in A and B of plate fig. i, a well developed columnar epithelium was 



