MENDELISM 65 



Cases of this same type have been met with in regard 

 to other characters of oats, and also in maize. 



A more complicated instance of the same kind has 

 been discovered by the same investigator. On crossing 

 a certain type of red wheat with a white variety, a 

 hybrid of intermediate shade was produced. On breed- 

 ing from this, all intermediate shades of colour were 

 produced, ranging from deep red to pure white. It is 

 impossible here to discuss fully the analysis of this case, 

 but Nilsson-Ehle has clearly proved that red colour in 

 the original parent was due to the action of three inde- 

 pendent dominant factors. Each factor alone produces 

 a certain amount of red colour ; moreover, the shade is 

 only half as deep when it is in the hybrid as when it 

 is in the pure condition. The result in the second 

 generation is that there are six possible shades of red, 

 besides the pure white, forming an almost continuous 

 series. Other consequences of the hypothesis of three 

 factors have been confirmed by experiment. This case 

 is one of the most complex that have yet yielded to 

 Mendelian analysis. 



An interesting complication of another sort has been 

 discovered with regard to leaf variegation in the garden 

 snapdragon (Antirrhinum). One variety of this plant 

 has its leaves dotted over with green and yellow, like 

 many other variegated forms. It has long been known 

 that this variety never breeds true, but always throws 

 a proportion of green " sports." On counting a batch 

 of plants, there were found 573 variegated, 286 green, or 

 almost exactly the ratio of 2:1. What could be the 

 meaning of this ratio ? 



On closer investigation of the seedlings, it was found 

 that the actual ratio was 1 green : 2 variegated : 1 

 yellow. A certain amount of green colour is well known 

 to be an essential of ordinary vegetable life, and the 

 yellow-leaved specimens all died as seedlings. The case 

 is therefore similar to that of the hybrid primula there 

 being produced 25 per cent, of each of the pure types, 

 and 50 per cent, of the hybrid form ; only in this 

 instance one of the pure types is incapable of living. 



