PI,ANT BREEDING 143; 



physiological and genetic. A method is also proposed by which physio- 

 logical and genetic correlations ma^^ be distinguished. Physical correla- 

 tions, are those in which the relation of cause to effect is evident, that is 

 to sa}^ in which one character is a function of another (for example when 

 an increase of weight is correlated with increased height). Physiological 

 correlations are those in which two characters are both the result of the 

 same phj'siological tendency, as when long internodes in the primary stem 

 are correlated with long internodes in the branches. Genetic correlations 

 comprise the large residue of correlations, the nature and causes of which 

 are subject to controversy, but which are associated with the method or 

 mechanism of heredity. In order to determine with certainty that a given 

 correlation is physiological and not genetic, it would be necessary to de- 

 monstrate the existence of the correlation in a number of subjects in which 

 all the individuals possessed the same hereditary tendencies with respect 

 to the characters studied. Theoretically this is only possible in asexually 

 propagated groups. Approximately pure lines can be obtained where 

 selfpolUnation is possible, so that if correlations are found, they may with 

 assurance be considered physiological. With maize, however, even ap- 

 proximately pure lines present such abnormal conditions that some other 

 method of study must be soiight. For tliis plant it would seem that the 

 solution of the question might be approached b}' comparing the degree 

 of correlation in types or varieties having a relatively restricted ancestry 

 with that in several generations of hybrids crossed among themselves and 

 derived from two contrasted types. An equally satisfactory^ method is 

 to compare the degree of correlation in the hybrid of the first generation 

 with that of the generations obtained by crossing the hybrids among them- 

 selves. If the first generation is all descended from a .single cross, its ga- 

 metic differences should be no greater than those of the progeny obtained 

 by self-pollination. 



The hybrid that afforded the data for the present paper was a cross 

 between " Waxy Chinese " and " Esperanza ", two varieties of maize 

 separated by a number of definitely contrasted characters. These extreme 

 types must have been completely isolated from very remote times. The 

 hybrid was made at Lanham, Md. in 1908. The plant of Waxy Chinese 

 used as female parent of the h^'brid was grown from the original seed 

 imported from China. The Esperanza variety belongs to a peculiar type 

 of maize {Zea Hirta of Bonafous) that appears to be confined to the table 

 lands of Mexico. The characters of the two varieties presenting the sharp- 

 est contrast are as follows. 



"Esperanza" " Waxy Chinese" 



Horny endosperm Wcxy endo?perni. 



Branching spact short Branching space long. 



Tassel erect Tassel curved. 

 Spikelets of the male inflorescence in whorls of Spikelets of the male inflorescence inserted in 



:: to 5. l)airs. 



Glumes long. <">lumes short. 



I,eaf sheaths with tuberculate hairs. IvCaf sheaths without tuberculate hairs. 



Upper leaf blades horizontal. Upper leaf blades erect. 



Upper leaf blades distichous. . Upper leaf blades monostichous. 



