MEXDELISM 71 



Odontoglossum and Cocbliod i), Miltonioda (a hybrid between 

 Miltonia and Cochlioda), Vnylslckeara (a multigeneric hybrid 

 lvt\\veu Miltonia and Odontioda), Laelo-cattleya, and others. (See 

 beginning of Ch'ipter, tinder Selection and suving of seed). 



MENDELISM 



The 1 iw of heredity known as Mendel's Law, discovered in 

 the sixties of the last century by the ABBE GREGOR MENDEL, has 

 now become almost a household word, and may be described as the 

 basis of scientific plant-breeding. Until this law was demonstrated 

 all breeding, or cross-breeding, was effected to a large extent in 

 the dark, and although as a general rule the peculiarities of the 

 present generation might reasonably be expected to reappear in the 

 progeny, what would actually happen could only be guessed at 

 beforehand. Often when crosses were attempted, although the 

 greatest care was exercised, no apparently successful result was 

 obtained, the progeny exactly resembling one parent only. MENDEL 

 conceived, however, the idea that the puzzling results of cross- 

 breeding must be governed by some settled law. He therefore 

 set himself to work to find it out, and in order to do so started his 

 experiments on the simplest lines he could conceive. He selected 

 the various forms of the edible or garden pea on the following 

 grounds : Firstly, the flowers of these are so constructed that from 

 the outset their anthers and stigmas are protected from outside 

 pollen (which, of course, would produce unwished for crosses) by 

 being enveloped in the keel of the flower, and by opening this keel 

 before the flower was fully grown, he could extract the unripe 

 pollen-bearing anthers and insert instead the ripe pollen he desired 

 to use, thus ensuring the desired cross. Secondly, these plants show 

 definite and distinct characters, such as differently coloured flowers, 

 and variously coloured and shaped peas, as well as pods. Finally, 

 as they are annuals, a fresh generation could be obtained every 

 year for the purpose of studying and tabulating results, and starting 

 fresh experiments. From these experiments MENDEL discovered 

 that the characters aforesaid fell definitely into two distinct cate- 

 gories, viz., (a) dominant and (b) recessive. A dominant character 

 is one which appears to the exclusion of the other in the immediate 

 offspring of a cross, the character which fails to appear being 

 recessive. 



The next discovery was that in a cross involving a dominant 

 and a recessive character ; all the offspring resembled the dominant 

 one, so that apparently the recessive parent had failed altogether 



