VARIATION 19 
That is, if measured and plotted the graph will approximate the normal 
curve of variability (Chapter III). Continuous variations are either 
heritable (combinations) or non-heritable (modifications) and, as was 
stated above, the only certain method of determining the class in which a 
Fig. 3.—Place-effects in common mustard (Brassica campestris) due to soil differences 
(herbarium specimens). 
given case may fall is the breeding test. Discontinuous variations are 
essentially discrete differences whether they be large or small. They 
are also either heritable or non-heritable and there is no correlation 
between size and heritability. Thus the extremely large and small 
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