Since cases of simple Mendelian phenomena have been very frequently described, the interest of the student of genetics has shifted from the attempt to prove, or disprove, Mendelism towards the investigation of the extent of the application of Mendel's fundamental principles. Perhaps this is why the apparent exclusion of anything Mendelian from size inheritance by Castle's work on the ear length of rabbits, aroused so much interest. Castle ('09) found that the ear lengths of rabbit offspring were in general'intermediate in relation to the parents. This seemed to indicate a simple blending inheritance in which the size-controlliig elements from either parent were permanently joined in the offspring, never to segregate. Yet in the same rabbits Mendelian ratios were being given and segregation was taking place in the color of the hair. The appearance of a paper by H.
Nilsson-Ehle ('09) brought a new possible interpretation of the ear length crosses. In this paper evidence was presented to show that there may be two or more Mendelian factors for the same character, which factors develop the character whether they appear alone or in any combination with the others.
Nilsson-Ehle found in certain crosses of oats and wheat in which the colors of the glumes and seeds were considered, that simple Mendelian ratios (3 : 1) were generally given, but in cer-This paper is based on an investigation carried on in the Laboratory of Genetics of the Bussey Institution with assistance from the Carnegie Institution of Washington. A full report of the investigation has been submitted to the Carnegie Institution for publication. This statement of some of its main features is published by permission. For the conclusions drawn from the facts recorded the author is alone responsible. 177