450 THE AMERICAN NATURALIST [VOL. XLII 



without difficulty by breeding tests, and these should be 

 made before any new principle is invoked, or the old and 

 well-founded principles are declared invalid, in the at- 

 tempt to account for such discrepancies. 



SUMMAKY 



The foregoing discussion and conclusions may be sum- 

 marized thus: 



In certain bean hybrids, mottled seed-coats depend 

 upon the presence of a mottling allelomorph in a hetero- 

 zygous condition, the homozygous condition giving un- 

 mottled seeds. This peculiar situation results in a tri- 

 polyhybrid ratio, 18:18:6:6:16, instead of the usual 

 ratio, 27:9:9:3:16. 



Latency is held to mean invisibility, and not inactivity 

 or dormancy, and four types are recognized, according to 

 the different causes of invisibility; still other types may 

 be found. The four types discussed in this paper are : 



(a) Latency due to separation, in which an allelomorph 

 when acting alone has no external manifestation and is 

 only rendered patent by combining it with another allelo- 

 morph. Such latency gives rise to the ratios 9:3:4, 9:7, 

 27:9:9:3:16 and 27:9:28, instead of the theoretical, 

 9:3:3:1 and 27:9:9:9:3:3:3:1. 



(b) Latency due to combination, in which two dominant 

 allelomorphs, each giving rise to a peculiar character 

 when acting alone, lose their external manifestation when 

 co-existing in the same zygote. Upon self-fertilization 

 this type of latency gives rise to such ratios as 1 : 1, 3:3:2, 

 18 : 18 : 6 : 6 : 16, etc., and may be found to account for the 

 existence of certain mid-races, and other cases in which a 

 double series of characteristics are presented in nearly 

 equal numbers. 



(c) Latency due to hypo stasis, in which the presence of 

 one allelomorph can not be detected owing to the presence 

 of another allelomorph, the character produced by the 

 latter being unmodified by the activity of the former. 

 This type of latency is exemplified by the black bean 



