492 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



yellows compared well with Professor Weldon's fig. 5, while the round 

 yellows were a full shade darker. (1902, pi. I.) 



In the same way fifty of the green round Peas were found to be indis- 

 tinguishable in colour from the pure green round 1 Eclipse ' grand-parent, 

 while the green wrinkled Peas were a full shade lighter. The wrinkled 

 greens compared well with Professor Weldon's fig. 1, while the round 

 greens were a full shade darker (1902, pi. L). It is evident therefore that 

 the round Peas, both yellow and green, are throughout the experiment a 

 full shade darker in colour than the corresponding wrinkled ones ; and 

 this apparently explains the fact of the dominant hybrids of the first 

 generation being a shade darker than the pure dominant, the former 

 being round while the latter was wrinkled. This suggests that the shade 

 of colour depends upon other factors than heredity, and it w r ould be 

 interesting to know why the wrinkled Peas are a lighter colour than the 

 round ones of similar breeding. Possibly the premature conversion of 

 starch in the wrinkled Peas (if it occurs) may have some effect on the 

 intensity of colour. 



In the above experiments the yellow and green colours are perfectly 

 discontinuous, with no trace of the intermediate shades of 1 Telephone ' 

 and ' Stratagem ' shown in Professor Weldon's colour scale (1902, pi. I.). 



Combination of Two Characters. 

 Seed Shape and Cotyledon Colour. 



Hitherto we have dealt with seed shape and cotyledon colour in Peas 

 as single characters, but the practical advantages of the Mendelian 

 principles become even more pronounced when we deal with two or more 

 characters in combination in individual plants or races. 



In the first generation the Wrinkled yellow ' British Queen ' was crossed 

 with the Round green 1 Eclipse,' and all the 19 hybrids were of one type, 

 Round yellow. 



In the second generation the Mendelian expectation is 4 distinct types, 

 viz. : Round yellow, round green, w T rinkled yellow, and wrinkled green, in 

 the respective ratios of 9:3:3:1. All the possible combinations are 

 effected, the frequency being according to the calculus of chance based on 

 the Mendelian ratios of 8 round to 1 wrinkled and 3 yellow to 1 green. 

 On the following page is a list of the actual numbers of each of the 

 4 types produced by the individual plants in Experiments 2-13. 



From the following table it will be observed that each of the expected 

 types occurs in the second generation in accordance with Mendel's law, 

 and that the numbers observed of each type are close to the numbers 

 calculated by means of the Mendelian ratios. The production of these 

 four types in the second generation proves that seed shape and cotyledon 

 colour are two distinct characters, each with a separate and independent 

 inheritance, and that each character must therefore be represented in the 

 germ-cellfl or gametes by a distinct unit. The appreciation of this 

 elementary fact enabled Mendel to make his discoveries in heredity. 

 All the statistical experiments in the heredity of animals and plants now 

 being carried on by many experimenters in Europe and America are based 



