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. 

 It is largely by keeping his eyes open and seizing upon 

 such sports for crossing purposes that the horticulturist 

 " 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. 



