XIII] Particoloured Peas 243 



According to the biometrical system, if the characters of 

 one parent and of the offspring are known, the material can, 

 after mathematical treatment by means of the correlation- 

 table, be used to deduce a law of inheritance. The theoretical 

 conceptions upon which this method is based were formed 

 and elaborated first in ignorance and subsequently in dis- 

 regard of Mendelian facts; but improbable as their validity 

 was in pre-Mendelian times, it must now be obvious that 

 these methods can merely obscure the essential phenomena 

 they were devised to discover. 



There are moreover abundant examples of other fluctua- 

 tions more obviously depending on environmental influences. 

 In studying the inheritance of the cotyledon-colours in the 

 seeds of peas such cases are met with. The cotyledons of 

 many varieties are in all ripe seeds a full yellow, while those 

 of many others are a full green. The contrast between the 

 yellow and the green seeds in /% after segregation may be 

 perfectly sharp and clear. Some varieties, especially the ^ 

 more modern sorts, have many seeds which are in various 

 degrees partly yellow and partly green, and occasionally 

 such particoloured seeds are the commonest type of the 

 variety. In his criticism of Mendel's work the late Professor 

 Weldon called attention to these particoloured seeds, con- 

 tending that they showed failure of segregation. Before 

 looking into the facts I was disposed to admit the justice 

 of this contention. After experimenting with such kinds 

 however I found that the particoloured appearance was 

 not caused by any admixture of the yellow character, but 

 by exposure to sun and weather. All those seeds which 

 tinge are by nature ^r^^;^ and breed true to greenness. It 

 in a pod several are found yellowed, this bleaching affects 

 those sides of the seeds which face the same wav and is 

 obviously due to effects of light just like the reddening of 

 the exposed sides of many apples. 



The hereditary property characteristic of these tinging 

 , sorts is the power of bleaching readily if exposed, but the 

 bleaching is checked and can generally be prevented if the 

 pods are gathered as soon as they are ripe. It may be 

 thought that the power of bleaching to which the ordinary 

 yellow varieties owe their colour is the same faculty inten- 

 sified. It may be so, but there are very marked distinctions ; 



16 — 2 



