84 



THE AMERICAN NATURALIST [Vol. LI 



experimentation. Here the facts are so recent and so 

 well known that a detailed review is unnecessary. I shall, 

 therefore, only attempt to deal with them, for the most 

 part, in a general way. Careful and critical selection ex- 

 periments may be said in general to have given opposite 

 results, according to whether the hereditary factors for 

 the character which formed the basis of the selection 

 were or were not positively known to be in a homozygous 

 condition in all the individuals of the race experimented 

 with. If the form used constituted a "pure line" in the 

 strict sense of Johannsen's conception, so that every in- 

 dividual was surely known to be strictly homozygous for 

 some state or condition of the character selected, and 

 the mode of reproduction was such as automatically to 

 retain and continue this condition, then the results of con- 

 tinued selection have in most cases been wholly negative 

 so far as the production of any change in type is con- 

 cerned. This is shown by the work of the Svalof Sta- 

 tion^^ with various cereals, of Johannsen^** with beans, 

 of Jennings'*^ with Paramecium, of Han el'' ^ with Hydra, 

 of Vilmorin^^ with wheat, of Ewing^^ with Aphis, of 

 Surface and PearP^ ^^i^h oats, of Fruwirth^^ with lentils, 

 peas, soy-beans and lupines, of Lashlej'*''^ with Hydra, of 

 Agar^^ with Simoceplialus, and of others. 



3»Cf. de Vries, H., loc. ext. passim, and Newman, L. H., "Plant Breed- 

 ing in Scandinavia." Ottawa, 1912. 



Linien." Jena, 1902. 



41 Jennings, H. S., Proc. Amer. Phil. Soc, Vol. 47, pp. 393-546, 1908 ; 

 and Amer. Nat., Vol. 46, pp. 487-491, 1912. 



42 Hanel, E., Jenaische Zeitschr., Bd. 43, pp. 321-373, 1908. 



43 Cf. Hagedoorn, A. L., and Hagedoorn, A. C, Zeitschr. ind. Ahst. Ter. 

 Lehre., Bd. XI, pp. 145-183, 1914. 



44Ewing, II. E., Biol. Bui., Vol. 26, pp. 25-35, 1914; and Ibid., Vol. 27, 

 pp. 164-168; and Ibid., Vol. 31, pp. 53-112, 1916. 



45 Surface, F. M., and Pearl, E., Me. Agr. Expt. Stat. Ann. Kept, for 

 1915, pp. 1-40. 



48 Fruwirth, C, Zeitschr. f. Pftanzemiichtung, Bd. Ill, pp. 173-225, 1915. 



4TLash]ey, K. S., Jour. Exp. Zool., Vol. 19, pp. 157-210, 1915; and Ibid., 

 Vol. 20, pp. 19-26, 1916. 



48 Agar, W. E., Phil. Trans. Eoy. Soc, London, B, Vol. 205, pp. 421-489, 

 1914. 



