78 PATTERNS AND PROBLEMS OF DEVELOPMENT 



plants and animals and their changes under experimental conditions have 

 been obtained, though largely with growing plants and adult animals.'^ 



It is evident from the data that potential gradients are characteristic 

 features of physiological axes, but different authors are not in complete 

 agreement as regards direction of change in sign. Mathews; Morgan and 

 Dimon; Hyman; Hyman and Bellamy; and Watanabe found in various in- 

 vertebrates a decrease galvanometrically in negativity from the apical or 

 anterior region basipetally or posteriorly and in annelids a second gradient 

 of negativity decreasing from the posterior end anteriorly to a certain 

 level. According to Lund and his co-workers, galvanometric positivity de- 

 creases from the apical region basipetally and increases again toward the 

 basal region of the hydroid Obelia. Also, the tips of stem axes of the 

 Douglas fir are galvanometrically positive (internally negative) to lower 

 levels, and in the onion root there is a decrease in galvanometric positivity 

 from the tip basipetally to a certain level with some increase farther basal- 

 ly. Barth, working with hydroids, does not find any constancy in direction 

 of potential difference. In Tuhularia the hydranth is negative to the mid- 

 dle stem region, and a cut or reconstituting end is usually negative to a 

 hydranth. In Eudendrium reconstituting regions are usually positive to 

 other regions. In this connection it may be noted that hydranth reconsti- 

 tution in Tuhularia is a redifferentiation of a portion of the stem without 

 outgrowth, while in Eudendrium and Ohelia outgrowth of tissue from the 

 cut end occurs before the hydranth develops. 



As regards hypotheses concerning the origin of bioelectric potentials, 

 Du Bois Reymond held that they originated in purely physical factors; 

 among the earlier physiologists, Hermann, Hering, Biedermann, and 

 Waller did not accept this view but maintained that they were associated 

 in some way with reactions of metabolism, though Hermann apparently 

 discarded this hypothesis later. In general, the hypothesis of a relation to 

 metabolism seems to have been regarded more favorably than others. 



'5 Numerous determinations have been made on plant axes, usually showing the tip elec- 

 tronegative to lower levels, a few with the reverse potential difference. The following refer- 

 ences are more or less directly concerned with axial potentials in animals: Mathews, 1903, 

 hydroids; Hyde, 1904, eggs of fish and turtle; Morgan and Dimon, 1904, earthworm; Hyman, 

 1918, 19326; Hyman and Bellamy, 1922, sponges, hydroids, hydromedusae, planarian, anne- 

 lids; Child and Hyman, 1926, hydroid; Lund, 1921c, 1922, 1923a, 1924a, b, 1930, 1931a, h, c, 

 1932a, b; Lund and Kenyon, 1927; Lund and Bush, 1930; Lund and Hanszen, 1931; Lund and 

 Moorman, 1931; Marsh, 1928, 1930, 1932; Rosene, 1930; Rosene and Lund, 1934, hydroids, 

 plant stems, and roots; Watanabe, 1928, earthworm; Burr, 1932; Burr and Lane, 1935; 

 Burr and Hovland, igsja, b, developmental stages of amphibia and mouse; Barth, 1934^, 

 hydroids; Hasama, 1935, artificially fertilized amphibian egg. 



