volume 13 Number 1 



The Plant World 



A Magazine of General Botany 

 JANUARY, 1910 



HEREDITY IN POPULATIONS AND IN PURE LINES. 



By L. R. Waldron. 



A contribution * on heredity in populations and in pure 

 lines from W. Johannsen, Professor of Plant Physiology at 

 Copenhagen, has recently commanded considerable attention, 

 and it seems worth while to present a brief review, even at this 

 late date, as the results are not generally accessible to American 

 students. Johnansen worked mainly with beans {Phaseolus 

 vulgaris) in pure lines. By a "pure line" is meant the offspring 

 of a single seed, known by the experimenter to have been so 

 derived. As bean plants are self-pollinated there was no trouble 

 in keeping the lines pure. 



Galton's researches upon the relations of oflFspring to parents 

 evidently acted as the stimulus to this piece of work; as his 

 studies of human stature and of sweet peas are particularly cited. 

 In his researches Galton secured a number of sweet pea seeds 

 and made weighings of them, and from these he selected seven 

 sets for planting. Plantings of these seeds were made in various 

 parts of England. 



The tabulated results from these experiments are shown 

 graphically in Fig. 1. * * The classes are the seed diameters 



♦Ueber Erblichkeit in Populationen und in reinen Linien, Jena, 1903. 



♦ *The relations between offspring and parents in regard to any character that may be 

 measured or weighed can be nicely expressed upon coordinate paper. We may let the vari- 

 able y represent some character of the parents while the variable x would represent the cor- 

 responding character of the offspring In the case of Fig. 1, we are dealing with the diam- 

 eters of sweet pea seed expressed in hundredths of inches. The mother seeds, which we 

 may consider as parents in this discussion, were grouped into seven classes, the diameters 



ranging from IS to 21 hundredths. The values of y,, yj, y-^ yj, are equivalent 



numerically to IS, 16, 17 21. The offspring of each of these classes were kept by them- 

 selves and the seed diameters ascertained. These are represented by the values Xi, xj, x j 

 x", and in this case are numerically equivalent to .153, .160, .156, .163, .160. .173, and 



