2 36 THE ORCHID REVIEW. 



HYBRID ORCHIDS AND MENDEL'S "LAW OF 

 INHERITANCE." 



" It is quite true that, according to Mendel's law, a plant may he a true 

 hybrid, although it presents only the ' dominant ' parental features, so that 

 all signs of the other, or ' recessive ' parent are invisible." 



This remark appears in a recent discussion about a hybrid Orchid, and 

 we have been asked how far Mendel's so-called " Law of Inheritance " is in 

 accord with the facts observed among hybrids generally. In the first place 

 we must deprecate the tendency to magnify into a so-called " Law " what 

 is at best but a provisional hypothesis, framed to account tor certain 

 phenomena observed among one class of plants, which, even there, 

 according to the observations of others, does not always apply, and which 

 completely breaks down when applied to many different groups. 



It is not certain that the plants which Mendel worked with are hybrids at 

 all in the true sense, it being extremely probable that they are only races 

 of a single species (Pisum sativum). Be this as it may, the essence of 

 Mendel's " Law," as we understand it, is that although a hybrid or cross- 

 bred presents a combination of characters derived from two diverse parents, 

 this combined character does not extend to the ultimate germ-cells, which 

 remain pure, and either transmit the one character or the other to the 

 offspring, not both. Mendel's deductions were that when twc races of peas 

 were crossed together, the offspring will exhibit the dominant characters 

 of the parents almost or quite unaltered, while other characters appear 

 to be missing, being present in such a slight degree as to pass unnoticed, 

 though the fact of their reappearance in a subsequent generation shows 

 them to have been latent; hence they are termed "recessive." This has 

 been termed the Law of Dominance. His second deductions were that 

 if these hybrids were self-fertilised, all the possible combinations of 

 the ancestral race-characters will appear in the second generation with 

 equal frequency, and these combinations will obey the Law of Dominance, 

 so that characters intermediate between those of the ancestral races will 

 not occur. This has been termed the Law of Segregation. The principle 

 is therefore deduced that in hybrids the ovules and pollen-grains retain 

 their originality throughout, the eventual combination of characters being 

 strictly confined to the number of combinations which may be possible 

 between the original ones, these retaining their integrity throughout all 

 transmissions. 



There are, however, large numbers of hybrids to which the remarks do 

 not apply. Hybrids may be divided into three groups, according to the 

 way in which they combine the parental characters. The great 

 majority may be termed intermediate, the parental characters being 



