6 4 
Notes on Recent Literature 
intermediate compound with C0 2 , or with carbon reserves in the 
bacteria themselves. The evolution of free nitrogen, under certain 
conditions, is in his view an argument for the existence of complex 
relations. 
As Niklewski’s initial cultures showed, the presence of agar 
in the culture medium enabled either organism alone to develop 
in 30% oxygen; he also found that 04% of either potassium tartrate 
malate, or formate, after an initial delay in development, had a 
similar effect, either organism alone developing as well as under 
the best symbiotic conditions. 
It is obvious that much remains to be done to solve the 
problems which Niklewski’s work has opened up; to decide 
between his and Lebedeff’s views on the physiology of these 
bacteria, and to explain the part they play in their natural habitat. 
It is not impossible that Lebedeff and Niklewski have obtained 
different bacteria, and that different relations hold for the different 
forms. D.T. 
GENETICS. 
Inter-Relations of Genetic Factors. 
Bateson & Punnett. “ On the Inter-relations of Genetic Factors.” 
Roy. See. Proc., B. Vol. 84, pp. 1—8, 1911. 
Bateson & Punnett. “ On Gametic Series involving Reduplication of 
certain Terms.” Journ. Genetics, Vol. 1, pp. 293—302, 1911. 
Recent investigations into the peculiar inter-relations which 
obtain between certain factors, when they are combined together 
in a hybrid, have given results of very great interest and signi¬ 
ficance, especially as regards their bearing on our conceptions of 
the nature of the phenomena which have hitherto been spoken of 
as “ coupling ” and “ repulsion ” of factors in the gametogenesis of 
hybrids. 
The present position of our knowledge of these phenomena can 
be most easily explained if we follow Bateson and Punnett (see the 
first paper cited above) in tracing the steps by which it has been 
reached. 
When a cross is made between parents differing in respect of 
two characters, A and B, the hybrid, which may be written AaBb, 
normally forms four kinds of gametes, namely AB, Ab, aB, ab. 1 In 
the simplest case these four kinds of gametes are produced in 
approximately equal numbers; but early in the investigation 
1 A and B indicate the presence ; and b the absence, of the 
factors which determine the characters. 
