KNOWLEDGE OF HEREDITY IN PISUM. 105 



hylum crossed with pale gave all dark in F 1, and in F 2 

 approximately 3 dark to 1 pale. 



4. — Characters of the Pod. 



Mendel described the inlieritance of two such pairs of 

 characters. 



(i.) The difference in the colour of the unripe pods, whether 

 greer or bright yellow. The former character was dominant, 

 and F 2 showed the usual proportion of 3 : 1 . I ara not 

 aware that any one has repeated this experiment in the case 

 of peas. But several observers have described exactly the 

 same phenomenon in Phaseolus. 



(ii.) The i)resence of the hard parchment layer in the pod 

 was described by Mendel as dominant to its absence — charac- 

 teristic of the sugar pea. Other observers, including the 

 present writer, have found the heterozygote to be more or 

 less intermediate in this respect. Segregation appears to 

 take place alwaj'^s in the normal way. 



Other pod characters also show segregation. Bateson 

 described the stumpy form of pod apex as being dominant 

 over the pointed, ard I have observed the same thing. 



As regards breadth of the pod, the F 1 plant bears pods 

 which are distinctly intermediate, but there are mdications 

 of segregation in F 2. 



In a note to his paper of 1865 Mendel stated that he was 

 starting experiments with the purple-podded pea, the pods of 

 which are of a deep purple colour when ripe. But no account 

 of these experiments was ever published. The offspring of a 

 considerable number of crosses between this variety and 

 various green-podded types have been examined by the 

 present writer, but the complexity' of the results has so far 

 precluded a simple description. The chief difficulty lies in 

 the existence of a high degree of fluctuating variability in 

 the degree of pigmentation among different pods borne by the 

 same plant. Apart from this, at least five different types of 

 plants appear in F 2. There are plants with fully pigmented 

 pods, and others with wholly unpigmented pods like the 

 parents. Then there are pods with the valves fully pigmented 

 at the margins and the central parts green, and others (on 



