7 o8 SCIENCE PROGRESS 



as already demonstrated, unfixable, and consequently the black 

 and white types of this may be neglected as valueless. Forms 

 with fully fertile or with rudimentary lateral florets breed true 

 from the outset, the recessive white character also breeds true, 

 so that the combination of white and either of these forms of 

 laterals should be fixed. Numerous trials have shown that 

 this is the case. The corresponding black forms might or might 

 not breed true, the complication being introduced by the fact 

 that the black may be either homozygous or heterozygous. 

 To isolate the homozygote it was, however, only necessary to 

 raise a further generation of these black types, sowing the 

 produce of each plant separately, when one in three was found 

 to breed true to the combination of blackness and either the 

 hermaphrodite or sesters lateral florets. 



It is thus clear that a plant breeder knowing these facts could 

 pick out in the generation raised from the hybrids the white 

 forms with either hermaphrodite or rudimentary lateral florets 

 knowing that these would breed true, and in the following 

 generation he could distinguish with certainty the corresponding 

 black forms. Until recently it would have been a difficult matter, 

 following the ordinary practice, to isolate these latter types in 

 a pure condition. A number of, say, the type with rudimentary 

 lateral florets would have been gathered at hazard and the seed 

 sown. The heterozygous blacks would throw off the recessive 

 whites, and though these would have been rogued out, a fresh 

 generation of heterozygotes would repeat the phenomena season 

 by season. In the same way no roguing would ever fix the 

 form with staminate lateral florets, for the possession of such 

 is, in this case, the mark of the heterozygote. On the contrary, 

 the recessive white, in combination with either of the forms of 

 the lateral florets which are characteristic of the parents, would 

 come true from the first — an illustration of the fact so puzzling 

 to breeders that some hybrid forms would breed true whilst 

 others of the same descent were unfixable. 



The fresh combinations of characters occurring in the parents 

 which are produced on hybridising are perfectly pure. Naturally, 

 owing to the briefness of the period for which such experiments 

 have been carried out, the matter has not been tested as 

 thoroughly as the hypercritical might wish for, and there is still 

 among practical people much suspicion as to the fixity of hybrids 

 — a view not to be wondered at when the seed lists contain 



