E. R. Saunders 321 



Numbers approximating either to the one ratio or the other were 

 similarly obtained when these F^ cross-breds were «e(/'-fertilised. These 

 results will be discussed later. (See Section V, and Table VII.) 



From these facts it seems clear that among these eversporting forms 

 self-breeding and inter-breeding give similar results. 



IV. Constitution of the zygote and segregation in the 

 eversporting forms. 



In any attempt to construct a formula which shall represent the 

 behaviour of the eversporting forms, so far as it is at present known, 

 the following points must be taken into account: 



(1) All the self-bred single descendants of an eversporting indi- 

 vidual appear to be also eversporting. 



(2) It also seems certain that all individuals of the eversporting 

 types employed yield an excess of doubles. The evidence points to 

 a proportion of 7 -I- ir single to 9 — a? double, the value of x being less 

 than 1. We may take it that the occurrence of such a ratio precludes 

 the possibility of the appearance of singles and doubles being determined 

 by the presence or absence of one factor only. 



(3) All the pollen grains of an eversporting individual apparently 

 carry doubleness, whereas the ovules are mixed, some carrying double- 

 ness and some singleness. 



(4) The inheritance of singleness and doubleness appears to be 

 quite independent of surface character (whether hoary or smooth) and 

 of the character of the sap (whether coloured or colourless), but in 

 certain cases, if not in all, it seems to be in some way bound up with 

 the inheritance of plastid character (whether white or cream). In the 

 present account therefore we may disregard surface character and sap 

 colour, but it will be convenient to consider plastid character simul- 

 taneously with that of singleness and doubleness. 



With regard to the conclusion given under (2) it may be noted that 

 where more than one factor is concerned in the manifestation of any 

 character it becomes theoretically possible for this character to appear 

 on crossing, even though both parents are breeding true in regard to 

 its absence. In a case, however, where the factors are not distributed 

 equally among pollen and ovules, this unequal distribution may in fact 

 prevent such a possibility, and this appears actually to be the case here. 

 As yet no mating between two true-breeding singles has ever produced 

 doubles. (For details of some of these cases see Report IV, Table III, 

 p. 40.) 



