The progress of Genetics since the rediscovery of Mendel's papers. 383 



Such a '"homostyle" crossed with a short-styled phmt gives F^ 

 which has typical short-styled flowers, with the characteristic large 

 pollen-grains and a small eye, the anthers being of course at the 

 top of the tube. In fact there are two pairs of characters of which 

 the first is in each case dominant. 



Dominant. Recessive. 



Thrum or Short-styled type Pin or Long-styled type 



Small eye. Large eye. 



Mr. Gregory and I found (8) that the F« from such a cross 

 consisted of four types, (a) Short style with small eye. (b) Short 

 style with large eye. (c) Normal long style with small eye. (d) Homo- 

 style with large eye. These forms occurred in the ratio 9a :3b: 

 3c: Id. 



The long styled form was not ptit in, but is made by that re- 

 combination of the characters, which occurs when the small eye is 

 present in a long styled flower. The homostyle is the form which 

 the pin-eyed type assumes when the plant is homozygous in the 

 large-eye character. 



Interaction between characters belonging to distinct allelo- 



morphic pairs. 



From the cases of novelties by recombination we pass to the 

 phenomena of interaction, the elucidation of which constitutes one of 

 the most important advances in the general development of genetics 

 made since the re-discovery of Mendel's work. There can be no 

 doubt that such interactions and their consequences pervade the 

 phenomena of inheritance, and are a far-reaching source of compli- 

 cation. These difficulties were first encountered in the attempt to 

 express the complexities of colour-inheritance in a simple Mendelian 

 system. For example, in several animals (Mice, Rats, Eabbits) it was 

 known that the albino form was recessive to all colours. When the 

 wild grey type was crossed with albino, F^ was wild grey. But the 

 composition of Fg was, not always the same. Sometimes F.^ consisted 

 of 3 greys : 1 albino, which is the simplest result. When however 

 other individuals were used as parents, more than one coloured type 

 might appear in Fg, for example there might be some greys and 

 some blacks. In such cases however the total of coloured individuals 

 was always 3, to 1 albino. Experience showed that the proportion 



Progressus rei botanicae I. 25 



