THE PRESENT POSITION OF THE THEORY OP ORGANIC EVOLUTION. 99 



But meanwhile another line of attacking the problem had 

 been developed, and one which led to quite different results. 

 An Augustinian monk named Uregor Mendel had been perform- 

 ing experiments on the crossing of different races of plants even 

 at the time that Darwin was putting the final touches to the 

 Origin of Species. He obtained most interesting results, but his 

 work remained unnoticed by his scientific contemporaries ; it was 

 not until 1900 that it was rediscovered. Then his experiments 

 were repeated and his results confirmed and extended, and a 

 large school of enthusiastic experimenters into the laws of 

 heredity along the lines mapped out by Mendel has grown up in 

 America and England. A popular idea has arisen that Mendel 

 has in some way refuted Darwin. It is therefore necessary to 

 look closely into what Mendel's results really were, and they can 

 be made quite clear by taking as example the pea plant, on 

 which Mendel's work was chiefly done. Numerous varieties 

 of peas exist ; thus, when ripe, dry peas may be yellow or green, 

 round or wrinkled. Now Mendel found that if the pollen from 

 a plant produced from a yellow pea were used to fertilize the 

 ovules of a plant produced from a green pea or vice versa, only 

 yellow peas were produced. If these yellow peas were then 

 sown, they produced plants which, when self -fertilized, gave rise 

 to yellow and green peas in the proportion of three yellow to one 

 green. 



Now in this cross Mendel termed yellowness the dominant 

 character, because it alone appeared in the hybrid or first filial 

 generation ; greenness was termed by him the recessive character 

 because it disappeared in the first filial generation, but reappeared 

 in the offspring of the hybrid, that is the second filial generation, 

 suffering therefore only a temporary eclipse. 



If the green peas which reappear in this generation be sown, 

 they give rise to plants bearing (when self-fertilized) only green 

 peas, and this is true however many generations may be raised 

 from them. Further, some of the yellow peas do the same ; but 

 two-thirds of them give rise to plants which, when self-fertilized, 

 produce yellow and green peas in the proportion of three yellow 

 to one green; in other words, they behave like the original hybrid 

 of the first filial generation. Mendel explained his results as 

 follows: When the first hybrid produces ovules and pollen 

 grains, these are of two kinds. One sort of ovule and of 

 pollen grain carries the yellow character, and another sort of ovule 

 and pollen grain carries the green character. These two kinds 

 are produced in equal numbers, and in self-fertilization they may 

 be supposed to be mixed at random. There is therefore one 



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