Variation and Heredity 



487 



for the tomato. These may serve as a further example 

 of unit characters, and they are listed below, the dominant 

 unit of each pair being placed in the middle column : 



Fruit Shape : 



Fruit Color 



Spherical or Round 

 Two-celled . . . 

 Roundish-conic 



Red Fruit . . . 

 Red Fruit . . . 

 Pink Fruit . . 

 Yellow Fruit Skin 



Pyriform 



Many-celled 



Roundish-compressed 



Pink Fruit 

 Yellow Fruit 

 Yellow Fruit 

 Transparent Fruit Skin 



Fruit Surface : Smooth Pubescent 



Foliage : Normal or Cut Leaf . Potato Leaf 



Pimpinellifolium Leaf Normal Leaf 



Green Leaf .... Yellow Leaf 

 Normal or Smooth 



Leaf Surface . . . Rugous Leaf 



Stature : Standard Stature . . Dwarf Stature 



298. Chromosome relations. A material basis for 

 certain types of inheritance, especially Mendelian phe- 

 nomena, seems to be found in the behavior of the chromo- 

 somes. The reduction division, occurring in seed plants 

 in the formation of the microspores (ultimately pollen) 

 and megaspores (ultimately embryo-sac) is the important 

 stage. In this the 2x (somatic or diploid number of 

 chromosomes is reduced to the x (gametic or haploid) 

 number. It is generally held that the essential features 

 of this division are two : (1) close association in pairs 

 (bivalent chromosomes) of paternal and maternal chromo- 



