128 White. 



partial expression of the A and B factors. In F2, the progeny are 

 divisible into 9 g-ametic classes in the proportion of 1 AABB : 2 AaBB : 

 2 AABb : 4 AaBb : 1 AAbb : 2 Aabb : 1 aaBB : 2 aaBb : 1 aabb. These 

 classes also represent the apparent or visible classes, because the 

 heterozygotes are distinguishable from the homozygotes. In practise, 

 accurate classification of the progeny into these classes was impossible, 

 owing to the presence of modifying genes in the two grandparental 

 races, which were also segregating in this Fa. The ratio of BB and 

 Bb to bb individuals in this Fa was as accurate as was to be expected, 

 but a great excess of apparently normal aa segregates occurred. Some 

 of these undoubtedly belong gametically to the other classes. Calyc- 

 anthemy is only slightly altered by the presence of modifying genes or 

 ordinary changes in external environment. This is to be expected, when 

 such a character is compared with one much more fundamental (in that 

 it expresses itself by such numerous and far-reaching alterations) in the 

 organism's life cycle, such as is true of fasciation. 



Gr. General discussion, sliowing tlie bearing of these 

 data on some of the more general problems of evolution 



and heredity. 



Under this heading, I wish to present certain general conclusions 

 which my data, in iiiy opinion, justify, The chief of these concerns the 

 latent character hypothesis of the morphologists, in so far as it bears 

 on problems of genetics and evolution. This conception, especially in 

 the form presented by de Vries is not only confusing, but actually 

 contrary to fact, as I have shown in the body of this paper. A further 

 example will, I hope, make my previous contention clear. The character 

 fasciation, as it occurs in Pisum, appears in at least two physiologically 

 distinct forms. In Pisum umhellatum it is absolutely hereditary under 

 the ordinary environments in wliich peas are grown. Lynch, Uimpau, 

 Koernicke, Mendel, Lock, as well as myself, all vouch for this fact. 

 Under these same conditions the ordinary varieties of peas do not 

 possess this character. But in a case reported by Blodgett (Fig. 28), 

 environmental phenomena induced this character in a variety of Pisum to 

 the extent that not more than 10 per cent of the plants remained normal. 

 This effect was distinctly an environmental one and was not hereditary 

 in the absence of the inducing agent. Blodgett was not able to show 



