August 3, 1917] 



SCIENCE 



115 



overcome. Sir George Savage referred to tlie 

 great amount of interest lie found in the old 

 herbals in his possession, although some of 

 them were difficult to follow. He had spent 

 four years in a very wide country practise in 

 Cumberland, and he recalled his indebted- 

 ness to a man who made a great many of the 

 simpler remedies from dandelions and other 

 plants, and saved a great deal of trouble. 

 British bed-straw was a useful herb; in the 

 British Medical Journal of forty years ago 

 he found a note on its efficacy in certain 

 cases. He concluded by quoting a remark of 

 Eousseau to the effect that the field of botany 

 had not been studied by scientists, but had 

 been exploited by medical men who wished 

 the public to have faith in their simples. 



SPECIAL ARTICLES 



THE CHEMICAL BASIS OF REGENERATION 

 AND GEOTROPISM 



1. It is a well-known fact that in many 

 plants after the removal of the apex some res- 

 toration of the old form is accomplished by 

 the growth of a hitherto dormant bud near the 

 wound. This process has been called regener- 

 ation. It is also well known that in certain 

 fir trees the old form is restored in such a case 

 in an apparently different way, namely by one 

 or more of the horizontal branches next to the 

 apex beginning to grow vertically upwards 

 (negative geotropism). One may wonder how 

 it can happen that the same result, namely the 

 restoration of the old form, is accomplished 

 in the organic world in such different ways; 

 and it is quite natural that occurrences of this 

 kind should suggest to one not a mechanist 

 the conception of mystic forces acting inside 

 or outside the living organism towards a 

 definite purpose, in this case the restoration of 

 the lost apex. The writer pointed out not 

 long ago that both phenomena, the restoration 

 of form of a mutilated organism by geotropic 

 bending as Tvell as by the growing out of 

 hitherto dormant buds may be caused by one 

 and the same agency; namely the collection 

 of certain chemical substances near the 

 wound.^ IRew experiments which the writer 



1 Loeb, J., SciEN-CE, 1916, XLIV., 210 ; Bot. Ga- 



has since made seem to prove this idea to be 

 correct. 



2. In a previous paper the writer had shown 

 that when an isolated piece of stem of Bryo- 

 phyllum calycinum, from 10 to 15 cm. long, 

 with one leaf attached to its apical end, is 

 put in a horizontal ijosition the stem will grad- 

 ually bend and assiune the shape of a U, with 

 the concave side upwards and that this bending 

 is due to the active growtli of a certain layer 

 of cells in the cortex on the lower side of the 

 stem. When the same experiment is made with 

 stems without a leaf attached some geotropic 

 bending of the stem still occurs, but at a much 

 slower rate. From this observation the writer 

 drew the conclusion that the leaf furnishes 

 material to the stem which causes the growth 

 of the cortex of the lower side of the stem, re- 

 sulting in the subsquent geotropic bending of 

 the stem.- The leaf forces this material into 

 that part of the stem which is situated more 

 basally than the leaf ; since the part of the stem 

 situated in front of a leaf does as a rule not 

 show any geotropic bending. The fact that 

 the growth leading to the geotropic curvature 

 takes place in the cells of the lower side of a 

 horizontally placed stem indicates that the 

 material causing the growth collects on the 

 lower side of the stem, which appears quite 

 natural, since this material is a liquid, ]X)S- 

 sibly containing some solid particles in sus- 

 pension. A slight leakage of sap from the 

 conducting vessels might be sufficient to ac- 

 count for such an accumulation of material 

 on the under side of a horizontally placed 

 stem. 



3. Since the publication of these observa- 

 tions on geotropism in Bryophylluni the writer 

 has been able to show that the mass of shoots 

 which an isolated leaf can produce from its 

 notches is a function of the mass of the leaf 

 and that sister leaves of equal size when iso- 

 lated from the stem produce equal masses of 

 shoots under equal conditions and in equal 

 time, even if the nimiber of shoots produced 

 differs considerably in the two leaves. Wlien 



zette, 1917, LXIII., 25; "The Organism as a 

 Whole," New York, 1916, p. 153. 

 - Loc. cit. 



