98 THE ORCHID REVIEW. [ApRIL, 1906. 
and it was found that while the recessives and pure dominants each bred 
true, the hybrid dominants segregated again into one recessive and three 
dominants, one of the latter again being pure while two remained hybrid. 
This was termed the “ Law of Purity,” and Mr. Hurst had also found in his 
experiments with plants and animals that the extracted recessives bred true, 
with no trace of the dominant ancestors. 
THE MENDELIAN THEORY. 
Mendel did not offer any explanation of the facts of dominance, nor has 
any satisfactory one yet been propounded. He, however, put forward a 
simple theory, namely the segregation of the gametes or germ-cells of the 
hybrid, so that on the average one-half of the gametes carry the dominant 
character and one-half the recessive; no gamete carrying both. This is 
known as the theory of gametic segregation or gametic purity. Thus the 
union of two gametes carrying the recessive character would result in a 
pure recessive, and the union of two carrying the dominant character would 
result in a pure dominant, while the union of dominant with recessive, oF 
the reverse, would again result in hybrids, in which, however, the recessive 
character would be masked, and thus they would appear dominants. These 
are therefore terméd “ Hybrid Dominants.” On the law of averages, each 
kind of union will occur with equal frequency, hence the result of twenty 
five per cent. pure dominants, fifty per cent. hybrid dominants, and twenty- 
five per cent. pure recessives, which is in close agreement with the results 
obtained by Mendel. The above explanation deals with a single character 
only, 
character, the actual problem is one of great complexity. 
As to the practical application of the Mendelian laws, Mr. Hurst con- — 
siders that when the points desired by the breeder coincide with the 
Mendelian characters a knowledge of these laws will enable him to get what 
he wants in the shortest possible time, as recessives breed true at sight, 
though several dominants might have to be bred from before the pure 
dominant was found. But if the desired point combined several Mendelian 
characters a much larger number of individuals will be required to secure 
the pure form, but once found it will breed true at once. Thus the breedet ; 
must rely on the assistance of the Mendelian experimenter. 
The facts of dominance show that the outward appearance of an 
individual is often no guide at all to a know 
i ledge of its breeding potentiali- 
ties, 
t and that a knowledge of its gametic constitution is the only guide t0 
its heredity, and this can only be secured by Mendelian analysis. 
The result of recent experiments show that the law of dominance 5 
apparently not universal, for in some cases the hybrid dominants do not 
minant parent, there being some traces of the q 
being i plet In other cases the 
exactly resemble the pure do 
recessive character, the domi 
but as the gamete or germ-cell may contain more than a single — 
