2 INHERITANCE OF SOME CHARACTERS IN WHEAT. 



as to the complex nature of the characters in wheat and the exist- 

 ence of more than one factor in characters which to the eye appear 

 simple. 



Nilsson-Ehle, starting from the standpoint of Bateson's pre- 

 sence and absence hypothesis, has obtained very interesting results at 

 Svalof. He bases his conclusions on a study of wheat and oats, and 

 the characters investigated in wheat were chaff colour, grain colour, 

 ear form and resistance to yellow rust. His conclusions are summed 

 up in the following paragraphs : — 



1. Characters which to the eye appear simple, for example, 

 the red colour of the grain or chaff, may be complex and may con- 

 tain two or more factors. These factors may exist independently 

 and each produces by itself a red colour and thus the red colour 

 in chaff or grain, even when simple, is not always due to the same 

 factor. When two red wheats are crossed, each containing several 

 red factors, one of which is common to both, the result, in the second 

 generation, is a series of red tones which, although distinct, defy 

 accurate classification. Thus when the factors are numerous, and 

 the differences between them are small, a continuous series of forms 

 would result in the F 2 . 



2. In the mode of inheritance there is no inherent difference 

 between qualitative and quantitative characters. In such quanti- 

 tative characters as resistance to rust or length of the internodes of 

 the rachis the behaviour of the various generations from the cross 

 indicate the existence of several factors. The difficulty in dealing 

 with the inheritance of physiological characters such as rust resist- 

 ance and with characters concerned with size is the want of an 

 analyser, that is, a wheat in which the particular character is totally 

 absent. In studying the inheritance of red colour factors, a 

 white wheat acts as an analyser. It is, however, impossible to use 

 a wheat without height or size in investigating characters dealing 

 with the dimensions of organs. Similarly, there is no absolutely 

 rust resistant wheat which can act as an analyser for the study of 

 the factors involved in this character. Both qualitative and quan- 

 titative characters may be complex and may be made up of several 

 factors which are inherited independently. 



