WHEN the apical shoot of a fir tree is broken o off or injured, it is a familiar fact that one of the lateral branches below changes its direction of growth in order to take the place of the original apical shoot. The change of direction is accompanied by greater vigour of growth. These phenomena attracted the attention of Errera,1 who suggested, as the reason why the lateral shoots do not tend to grow vertically while the apical shoot is intact, the possibility that the latter might produce inhibitory substances of a chemical nature which travel downwards to the other parts of the tree. Direct evidence was not then available, but the hypothesis has since received confirmation from certain experiments by Dr. Jacques Loeb, who appears to have been unaware of Errera's suggestion.
Brit. Ass. Reports, 1904, p. 184. "Conflits de préséance et excitations inhibitories chez les végétaux," Bull. Soc. roy. botan. belgique, vol. xlii., 1904; reprinted in "Œuvres Physiol. Gén"., p. 101. (Bruxelles, 1910.)
"The Chemical Basis of Axial Polarity in Regeneration". By Jacques Loeb. Science, N.S., vol. xlvi., p. 547. (1917.)
"Rules and Mechanism of Inhibition and Correlation in the Regeneration of Bryophyllum Calycinum," Botan. Gazette, Vol. lx., p. 249. (1915). "Chemical Basis of Correlation. I. Production of Equal Masses of Shoots by Equal Masses of Sister Leaves in Bryophyllum Calycinum," ibid., vol. lxv., p. 150 (1918.)
"The Law Controlling the Quantity and the Rate of Regeneration," Proc. Nat. Acad. Sci., vol. iv., p. 117. (1918.)
"Influence of the Leaf upon Root Formation and Geotropic Curvature in the Stem of Bryophyllum calycinum and the possibility of a Hormone Theory of these Processes," Botan. Gazette, vol. xliii., p. 25. (1917.)
"The Chemical Basis of Regeneration and Geotropism," Science, Vol. xlvi., p. 115. (1917.)
"The Chemical Regulation of the Secretory Process," Proc. Roy. Soc., vol. lxxiii., p. 310. (1904.)