castle. — mendel's law of heredity. 547 



of purity of the germ-cells. For the hybrid is like neither parent, but 

 the characters of both parents exist in a stable union in the mature germ- 

 cells produced by the hybrid. 



(c) Coupling (i. e., complete correlation) may exist between two or 

 more characters, so that they form a compound unit not separable in 

 heredity, at least in certain crosses. 



(a?) Disintegration of characters apparently simple may take place in 

 consequence of cross-breeding. 



(e) Departures from the expected ratios of dominants to recessives 

 may be explained in some cases as due to inferior vigor, and so greater 

 mortality, on the part of dominants or recessives respectively. 



(f) Cases of apparent reversal of dominance may arise from " false 

 hybridization " (induced parthenogenesis). Possibly in other cases the 

 determination of dominance rests with circumstances as yet unknown. 



5. Mendel's principles strengthen the view that species arise by dis- 

 continuous variation. They explain why new types are especially vari- 

 able, how one variation causes others, and why certain variations are so 

 peristent in their occurrence. 



Bibliography. 



Bateson, W. 



:02. Mendel's Principles of Heredity, a Defence. With a Translation 

 of Mendel's Original Papers on Hybridisation. 12mo, 212pp. 

 Cambridge. [England. Contains bibliography and portrait of 

 Mendel.] 

 Bateson, W., and Saunders, E. R. 



:02. Experimental Studies in the Physiology of Heredity. Reports 

 to the Evolution Committee of the Royal Society. Report I. 

 160 pp. London. 

 Correns, C. 



:00. G. Mendel's Regeln iiber das Verhalten der Nachkommenschaft 

 der Rassenbastarde. Ber. deutsch. bot. Gesellsch., Jahrg. 18, 

 pp. 158-168. 

 Mendel, G. 



:66. Versuche iiber Pflanzenhybriden. Verh. Naturf -Vereins in Brunn, 

 Bd. 4, Abh., pp. 3-47. [Translation in Bateson, :02 ] 

 Mendel, G 



:70. Ueber einige aus kiinstlicher Befruchtung entnomennen Hiera- 

 cium-Bastarde. Verh. Naturf. -Vereins in Bruini, Bd. 8, Abh., 

 pp. 26-31. [Translation in Bateson, :02.] 



