DEGENERATrON OF VARIETIES 317 



Investigation has shown that thin-stemmed races of barley 

 always give the best quality of grain JFor malting purposes, and to 

 breed a variety combining very high quality of grain with great 

 stiffness of straw is probably impossible. 



It is generally known that seed-production and luxuriance of 

 vegetative organs are mutually antagonistic; for example, with 

 high yield of tubers of good quality, seed-production in the 

 potato has been vastly reduced, and in the case of oats and 

 wheat short-strawed varieties usually give a greater proportion of 

 grain than long-strawed kinds. A turnip of slow, long-continued 

 growth yields a greater dry weight per acre than a rapid-growing 

 variety, for there is a greater time for the manufacture, accumula- 

 tion and assimilation of food in the former than in the latter; 

 the attempt to produce a variety of turnip of rapid growth and 

 high feeding-value would fail after a certain point of excellence 

 was reached; fortunately in this case there appears plenty of 

 room for systematic work and improvement before the limit is 

 attained, and the same is probably true of practically all farm 

 plants for very few well-organised attempts have been made to 

 improve them. 



6. Reversion, ' thro wing-back,' atavism : degeneration of 

 varieties. — A new variety of a plant becomes gradually estab- 

 lished and ' fixed' by destroying all those individuals of each 

 generation which do not resemble the general type. ' Fixation ' 

 is, however, a relative term, for even in cultivated varieties in 

 which the process of destruction has been systematically carried 

 out and which have 'come true,' from seed during many 

 generations, '■false plants' or ^rogues' departing considerably 

 from the type appear among the offspring at irregular in- 

 tervals. 



For example, individuals resembling the wild pansy ( Viola 

 tricolor L.) in form, colour and size of the flowers and leaves, 

 occasionally make their appearance among plants raised from 

 seeds of the best large-flowered cultivated types of pansy ; and 



