In Mr Biffeu's paper on “Mendel's Laws of Inheritance and Wheat Breeding” in the first number of this Journal reference is made on page 40 to the characters of immunity and susceptibility to the attacks of yellow rust. Mr Biffen's experiments confirm the conclusions of other observers, such as Farrer in Australia, that resistance and susceptibility to rust are inherited characters, and he shows that they follow the Mendelian laws. As the question is of enormous practical importance in the wheat growing countries this general statement requires to be made more precise. It holds for a given rust in a particular locality; it may or may not hold where the wheat is exposed to the attacks of a second species of rust or when it is transferred to another locality. Thus experience in India so far seems to show that resistance to yellow rust, Puccinia glumarum, does not imply resistance to orange rust, P. tritidna. And it is certain that the characters alter with change of locality.