THE NATURE OF THE DIRECTIVE INFLUENCE OF 

 GRAVITY ON THE ARRANGEMENT OF ORGANS 

 IN REGENERATION. 



By JACQUES LOEB. 



{From the Laboratories of The Rockefeller Institute for Medical Research.) 



(Received for publication, January 16, 1920.) 



In preceding papers it has been shown that gravity has a directive 

 influence on the arrangement of certain organs in the regeneration of 

 Bryophyllum calycinum. Thus, when an excised piece of stem of 

 Bryophyllum is suspended horizontally in moist air, roots will grow 

 abundantly on the lower side of the stem but not on the upper side, 

 with the exception of the basal end where the roots will grow on 

 both sides. In order to get abundant root formation it is necessary 

 to preserve one of the apical leaves on such a stem since the leaf 

 furnishes most of the material for the growth of the roots.^ 



A second case in which this directive influence shows itself is the 

 leaf of the same plant. When we suspend an isolated leaf of Bryophyl- 

 lum (in moist air) sidewise, in a vertical plane, roots and shoots will 

 grow abundantly in the notches of the lower side, but less abundantly 

 and frequently not at all in the notches of the upper side of the leaf 

 (Fig, 1 , upper row) . This phenomenon was explained by the writer 

 in the following way. Gravity causes a slightly greater collection 

 of sap on the lower side of the organs mentioned and this causes the 

 dormant buds for root formation to grow out a little earlier or more 

 quickly on the lower than on the upper side of the stem or the leaf. 

 It is a general rule in the phenomena of regeneration in Bryophyllum 

 that organs which grow out first or more quickly attract for some 

 reason the flow of sap (possibly by modifying the direction of the sap 

 flow) and thereby inhibit or retard the growth of similar organs in 

 other places, and this inhibitory factor is added to the influence of 



1 Loeb, J., /. Gen. Physiol., 1918-19, i, 687. 



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