84 MENDELISM chap. 



standard ; in other words, the arrival of the new form 



would give us the possibility of fourteen varieties instead 



of seven. As we know, the hooded character already 



exists. It is recessive to the erect standard, and we have 



reason to suppose that it arose as a sudden sport by the 



omission of the factor in whose presence the standard 



assumes the erect shape characteristic of the wild flower. 



fit is largely by keeping his eyes open and seizing upon 



I such sports for crossing purposes that the horticulturist 



Ll^ improves" the plants with which he deals. How 



(-these sports or mutations come about we can now sur- 



) mise. They must owe their origin to a disturbance in 



the processes of cell division through which the gametes 



originate. At some stage or other the normal equal 



distribution of the various factors is upset, and some of 



the gametes receive a factor less than others. From the 



union of two such gametes, provided that they are still 



capable of fertilisation, comes the zygote which in course 



of growth develops the new character. 



Why these mutations arise : what leads to the sur- 

 mised unequal division of the gametes: of this we know 

 practically nothing. Nor until we can induce the pro- 

 duction of mutations at will are we likely to understand 

 the conditions which govern their formation. Never- 

 theless there are already hints scattered about the recent 

 literature of experimental biology which lead us to hope 

 that we may know more of these matters in the future. 



