INCOMPATIBILITY 



carries a gene, an incompatibility gene, also present in the style. 

 Completely incompatible pairs of plants will then always be such 

 as have both allelomorphs the same. Compatible ones will be such 

 as differ in respect of one or both (Fig. 59). 



/Vt\ 





SEED 



Fig. 59. — Diagram showing the physiological relationship between pollen and style 

 and the genetic relationship between parent and offspring with homomorphic 

 incompatibility. Sj S.j styles receive, (i) self or similar pollen on the left and their 

 ovules remain unfertilized, (ii) in the centre mixed pollen part of which, if in 

 sufficient quantity, can fertilize all ovules, and (iii) on the right wholly compatible 

 pollen all of which can fertilize the ovules. 



Note. — No progeny can be incompatible with their mother, but in the middle case 

 a half will be incompatible with their father. 



This explanation suggested by Prell in 1921 was confirmed, a few 

 years later, by East and Mangelsdorf with Nicotiana alata and by 

 Filzer with Veronica syriaca. On its basis the inheritance of incom- 

 patibility has been successfully predicted in a large number of diploid 

 plants, hideed the mechanism probably occurs in some stage of 

 development or decay in about half the species of flowering 

 plants. 



MS 



