392 COOK 



holds for a time at a point of high expression a character which 

 averages much lower in the species at large. 



MUTATIVE VARIATION OF SELECTED VARIETIES. 



The only way in which the accentuation of such a narrowly 

 selected character can be still further increased, beyond the 

 range of normal variation of the species, is by abnormal varia- 

 tion ; that is, by mutation. The narrow selection may be said 

 to induce the mutations because it weakens and unbalances the 

 hereditary tendencies of the variety, but the mutations are by 

 no means limited to the character or quality for which the 

 variety has been selected ; they are likely to take any or all 

 directions. Some of them are generally found to carry the 

 breeder along the lines he desires to follow. 



Are hybrids between selected varieties of the same plant or 

 animal of no practical breeding utility? Yes, if it is desired to 

 preserve or strengthen the vitality of the organism or to secure in- 

 termediate characters, or new combinations of characters already 

 existing. 



The general answer must be negative, if the purpose is to 

 obtain new characters, or higher degrees for accentuation of 

 characters already specialized by selection. Instead of securing 

 a larger range of diversity, the contrary results are much more 

 likely to be reached. It may even happen, if the varieties have 

 been subjected to narrow selection, that the hybrid offspring, 

 instead of being more variable than their parents, will actually 

 be more uniform, the hybridization bringing them back, as it 

 were, to the hereditary road from which they were beginning to 

 wander towards mutative degeneration. 



The mutations are as abnormal, of course, in the strictly evo- 

 lutionary sense, as the narrow descent which induces them, but 

 for agricultural purposes they may be very valuable, and often the 

 abrupt change of form seems to lend them a remarkable vegeta- 

 tive vigor which greatly increases their productive capacity. 

 This is notably the case among plants, and especially among 

 those cultivated for their vegetative parts instead of for their 

 seeds. 1 



'Cook, O. F., 1904. The Vegetative Vigor of Hybrids and Mutations. Proc. 

 Biological Society of Washington, 17 : 83. 



