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SCIENCE 



IN.S. Vol. XXV. No. 647 



tains latent purple and latent mottling. 

 Tschermak" takes just the opposite view, how- 

 ever, and would say that the purple mottling 

 is latent in the pigmented bean, and that the 

 white bean acts simply as a releasing agent 

 which allows the latent character to become 

 manifest. Bateson^^ also subscribes to the 

 same view. On Tschermak's hypothesis it 

 would appear to me a remarkable coincidence 

 that the black, brown and yellow varieties 

 should all contain the same latent characters, 

 and I am forced to the conclusion just stated, 

 that the novelties which appear in these hy- 

 brids are directly derived from the white 

 parent. The new characters thus lose the 

 mystery that otherwise invests them. They 

 appear not as released prisoners or awakened 

 sleepers, which had for some inconceivable 

 reason remained inactive, but are combination 

 phenomena. 



The color characters of these beans are not 

 dependent upon a single pair of units, but 

 upon three pairs, viz. : 



1. Pigment vs. no pigment. 



2. Modifier which changes pigment to 

 purple vs. no modifier. 



3. Mottled color pattern vs. self color. 



Of these three characters, the brown and 

 yellow beans contain only the dominant pig- 

 ment character and might be represented by 

 the formula, Phm; the black bean contains 

 the pigment and the modification to purple, 

 PB'm; and the white bean contains both the 

 modifier and the mottled color-pattern but no 

 pigment, pBM. It is only because of the lack 

 of pigment that these two characters possessed 

 by the white bean are not apparent. They 

 are latent only in the sense that they are 

 invisible. Whenever the ' White flageolet ' 

 is crossed with any variety of self-colored 

 bean, the three dominant allelomorphs, PBM, 

 are brought together with the result seen in 

 these hybrids, namely, a first generation char- 

 acterized by dark purple mottled seeds. 



'° Tschermak, E., loc. cit. 



" Bateson, W., Saundera, Miss E. R., Punnett, 

 R. C, ' Experimental Studies in the Physiology of 

 Heredity,' Second Report to the Evolution Com- 

 mittee of the Royal Society, London, 1905. 



The great advantage of this explanation 

 over that of Tschermak is that it brings these 

 apparently aberrant results into harmony with 

 typical Mendelian cases, and allows with a 

 reasonable degree of accuracy, a prediction as 

 to the composition of subsequent generations. 



On the assumption that the F^ hybrids be- 

 tween the ' White flageolet ' and either of the 

 non-purple self-colored beans contain the three 

 dominant allelomorphs, PBM, associated with 

 the corresponding recessive allelomorphs, phm, 

 the following forms and proportions may be 

 expected in the second generation. In each 

 64 plants belonging to the second generation 

 there should be 



27 PBM ;= purple mottled like F^. 



9 PbM = brown mottled or yellow mottled. 



9 PBm = purple self-colored or black. 



9 pBM ^ white, exactly like the white parent. 



3 Pbm = brown or yellow self-colored. 



3 pBm ^ white (with the modifier but no mot- 

 tling) . 



3 pbU = white (without the modifier but with 

 mottling) . 



1 pbm ^ white (with neither modifier nor mot- 

 tling) . 



Owing to the fact that the internal com- 

 position of the white beans has no external 

 manifestation, the four white classes having 

 different allelomorphie composition are indis- 

 tinguishable from one another, thus . resulting 

 in a frequently found ratio for tripoly- 

 hybrids, 27:9:9:3:16. 



In this interpretation of latent characters 

 are to be found explanations of several observed 

 phenomena. Tschermak, Bateson and Emer- 

 son have noted that the behavior of a given 

 character in one strain can not be used safely 

 as a criterion for predicting the behavior of 

 an apparently like character in another strain. 

 A good illustration of this is seen on com- 

 paring with these hybrids of the ' White 

 flageolet ' bean, Emerson's cross between the 

 ' Ultra ' and ' Marrowfat,' the latter being like- 

 wise a white bean. The F^ hybrids were 

 brown mottled, thus showing that the ' Mar- 

 rowfat ' differs from the ' Navy ' or ' White 

 flageolet ' in having no dominant pigment- 

 changing allelomorph. The gametic formula 

 of the ' Marrowfat ' is, no doubt, phM, and 



