CONSEQUENCES OF CHANGE 



cated fragments or more complex changes. Allopolyploids are 

 derived from hybrids of all such types and by successive additions 

 appear as tetraploids, hcxaploids and so on. Their increase of number 

 generally increases their size. Their combinations of characters fit 



Ml 



2x 



4 



X 



FERTILITY IN POLYPLOIDS 



AUTO- 



ALLO- 



Lr 



/copersicunK 

 escuhntiinu 



Primula 



I\oJ>hano-' 

 brossiea 



<- 



■< 



In 



crccisi 



"A 



>■ 



-> Ferftlify 



Fig. 35. — Pairing at mciosis in diploids of different degrees of hybridity and 

 scgregational sterility compared with that in the tetraploids derived from them: 

 to illustrate the law of the negative correlation of fertility in diploid and tetraploid. 



them for new conditions, fit them for colonization. Occasionally 

 they segregate differences by accidental pairing of chromosomes 

 from the ultimate diploid parents and this also gives them 

 adaptability. But yet they remain highly fertile. It is not surprising, 

 therefore, that a large proportion of the species of flowering 

 plants owe their origin to alloploidy, and more especially a 

 large proportion of the new types of plants that have covered the 

 cultivated part of the earth in the last 10,000 years {cf., Fig. 82). 



140 



