1914] CURRENT LITERATURE 91 



ive is (1) for positive response, tartrate>citr.>S0 4 >acet.>C10 J >Cl>N0 J >J 

 >CNS; Rb>Cs>K>Li>Na; (2) for negative response, (a) for alkali salts, 



acet.>tartr.>J>Cl>Citr.>C10 3 >CNS>S0 4 >N0 3 ; Na>Li>K>Cs>Rb; (b) for 

 salts of alkali earths, J>Br>acet.>CL; Mg>Ca, Ba, Sr. 



The bromide and perhaps the iodide of alkali earths do not produce the 

 positive response. For negative chemotropism, salts of alkali earths are about 

 10 times as effective as those of the alkalies. Porodko believes from the 

 relative effectiveness of ions that the negative excitation involves coagulation 

 of cell lipoids as well as proteins, and that both the positive and negative 

 irritability are lined up with change of condition of cell colloids. Our knowl- 

 edge in this field is too limited, however, to follow the parallel in any detail. 

 William Crocket*. 



A theory of evolution. — Lest we forget that the method of evolution 

 remains undemonstrated, that evolution itself is somewhat of a scientific 

 dogma, it is desirable occasionally to have our attention called to the fact that 

 scarcely two even of the clearest-headed of our contemporary thinkers hold the 

 same views regarding it. Read Bergson, Butler, DeVries, Semon, Weis- 

 mann. Their works are lawyers' briefs, written to uphold the importance of 

 a single possible evolutionary cause to the greater or less neglect of all others; 

 but they are remarkable briefs for all that. Evolution is due entirely to a 

 directive force within the organism; evolution is due wholly to imperfections 

 in the machinery of heredity and has no directive aim whatever; evolution is 

 due solely to external causes; it is gradual, it is discontinuous; it is continual, 

 it is periodic. One is often led to believe that no middle ground, no com- 

 bination of methods is possible; moreover, it is often the individuals that strum 

 continually on a few notes, who force recognition of tunes labeled conspicuously 

 with their own personalities, by loud and persistent reiteration. 



The latest writer to be enrolled as an exponent of a unique cause of evo- 

 lution is Lotsy. 8 The unique cause is hybridization and the author's brief 

 has been extraordinarily well done. As the paper is introduced by the follow- 

 ing statement, the words "unique cause" do not exaggerate the position taken: 



Toutes les theories de revolution, y compris celle de Lamarck, Darwin et DeVries, 

 s'appuient sur Phypothese, ou sur la pretendue preuve, qu'il existe d'une fa?on ou 

 d'une autre une variabilite hereditaire. Le present travail a pour but de prouver que 

 cette hypothese se base sur une erreur; qu'il n'y a pas de variabilite hereditaire, sous 

 aucune forme, mais que les expeces sont constantes. 



Lotsy does not believe that Linnean species are constant, but that forms 

 truly homozygous are constant. His outline of the growth of evolutionary 

 belief shows this. 



A. The period when it was believed that the characters of an individual were trans- 

 mitted as a whole. 



8 Lotsy, J. P., La theorie du croisement. Arch. Xeerland. Sci. Exact, et Xat. 

 Ill B 2:1-61. 1914. 



