INFLUENCE OF THE LEAF UPON ROOT FORMATION 



AND GEOTROPIC CURVATURE IN THE STEM OF 

 BRYOPHYLLUM CALYCINUM AND THE POSSIBIL- 

 ITY OF A HORMONE THEORY OF THESE PRO- 



CESSES 



Jacques Loeb 



(with thirty figures) 



In two former publications 1 it was shown that while the stem 

 of Bryophyllum calycinum prevents or retards the development of 

 roots and shoots in the notches of a leaf, conversely the leaf acceler- 

 ates the development of roots and shoots in a stem ; since in a stem 

 deprived of all leaves the roots and shoots develop later and grow 

 more slowly than if a leaf is left on the stem. The two phenomena 

 found a common explanation in the assumption that the leaf 

 furnishes substances to the stem which accelerate the organ forma- 

 tion in the latter, while if these substances are not "sucked away" 

 from the leaf by the stem they will accelerate the growth of roots 

 and shoots in the notches of the leaf. These substances may be 

 water or solutes. 



In these experiments it was noticed that the leaf has also an 

 accelerating effect upon the geotropic curvature of the stem. 

 When stems of Bryophyllum are suspended horizontally by 2 

 threads in a jar saturated with water vapor, they will bend, becom- 

 ing convex on the lower, and concave on the upper side (fig. 1), 

 and this bending continues until finally the stems assume the shape 

 of a U. This geotropic bending is a slow process when the stem 

 contains no leaf, but is considerably accelerated if a leaf is left on 

 the stem (fig. i). The position of the leaf has a great influence, 

 not only on the velocity of the geotropic bending and the region of 

 the stem in which it occurs, but also upon the formation of organs 

 in the stem. The description of this influence and of the appar- 

 ently close connection between the two groups of phenomena will 

 form the subject of this paper. 



j Loeb, J., Bot. Gaz. 60:249-276. 1915; 62:293-302. 1916. 



25] 



[Botanical Gazette, vol. 63 



