INTERNAL CAUSES 529 



and in some animals, maleness and horns are associated. In some 

 varieties of Sweet Peas, round pollen is associated with red flower, 

 red flower with hooded standard, and sterile anthers with light 

 axils. In Primula, red stigma is associated with red flowers and 

 dark stem. Pubescence on certain regions of the grain and black 

 color of the grain are associated in Oats, and purple aleuron layer 

 and starchy endosperm are associated in some varieties of Corn. 

 In both plants and animals many linked characters are known. 



Occasionally, in the pairing and separating of chromosomes in 

 the reduction division there apparently occurs an exchanging of 



Fig. 474. — Representatives of the parents and of the Fj generation of a 

 cross between the Summer Crook-neck Squash and Field Pumpkin. Summer 

 Crook-neck Squashes are shown in the foreground and a Field Pumpkin is 

 shown at the right. The F2 individual at left resembles the Pumpkin in 

 shape, size, and color, but has some warts, thus resembling Crook-neck 

 Squash in this respect. The other F2 representatives have characters of both 

 parents but take after parents in different ways. Some are much more warty 

 than their warty parent. 



factors between the paired chromosomes. Some of the factors of 

 a mother chromosome of a pair become attached to the father 

 chromosome and the father chromosome loses some of its factors 

 to the mother chromosome. This of course results m the separa- 

 tion of factors commonly occurring associated, and in the forma- 

 tion of gametes with factors associated that are not usually 

 associated In the offspring arising from the fusion of gametes m 

 one or more of which unusual combinations of factors have 

 occurred unusual combinations of characters and thereby varia- 

 tions result in the offspring. Thus for example, in crossing 

 varieties of Sweet Peas round pollen commonly associated with 



