370 EXPERIMENTAL STUDY OF INHERITANCE 



smooth maize seed, is a consequence of its greater content of 

 water in the fresh state, and this again is a consequence of the 

 fact that the seed has dextrin and sugar instead of starch as the 

 reserve material for the embryo. Thereby a difference in weight, 

 in colouring, and in texture is brought about. All these features 

 depend upon a single primordium or rudiment — namely, whether 

 the seed contains dextrin and sugar or starch " (1905, p. 15). 



4. The idea of unit characters must be kept in harmony with 

 the indubitable facts of physiological correlation, and the idea of 

 their " independence " must be large enough to include the 

 fact that they seem sometimes to go in inseparable couples. 



In many ways, therefore, Weismann's somewhat subtler and 

 more complex conception of determinants which work out a 

 character by co-operative development appears to us to fit the 

 facts better. 



A New Yiew of EYolution. — As is well known, Darwin believed 

 that specific differences and adaptations were slowly brought 

 about by the consistent selection of small continuous variations 

 in a profitable direction. He did, indeed, recognise that large 

 discontinuous variations may suddenly arise, as in the case of 

 the short-legged Ancon sheep. He could not, however, lay stress 

 upon such occurrences, believing as he did that they were of 

 rare occurrence, and therefore very liable to be swamped by 

 intercrossing with the normal forms. 



Over and over again, both before and after Darwin, naturalists 

 had suggested that sudden emergences of new structures with 

 no small degree of completeness, brusque transitions from one 

 position of organic equilibrium to another, might be of evolution- 

 ary importance. We need only mention Etienne Geoffroy 

 Saint-Hilaire and Francis Galton. But the difficulty always 

 was, that these discontinuous variations seemed to be of rare 

 occurrence, and liable to be swamped. 



In 1894 Bateson showed in his Materials for the Study of 

 Variation that discontinuity in variation was a fairly common 



