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47 



MENDEL AND HIS LAW 



hand, always produced wrinkled peas. It was Mendel's problem to cross these 

 peas. Opening up a blossom before it was ready to bloom, Mendel cut the 

 unripe stamens out of the flower, thus removing the fertilizing element, placed 

 upon the pistil of these flowers pollen from a pea blossom of the other kind, and 

 protected the flower from accidental cross-poUination by insects. He found it 

 made no difference whether he carried pollen from a plant that bore wrinkled 

 peas to the pistil of a plant bearing round peas or made the reverse cross. The 

 result was always the same. The peas were always round. None of them 

 showed the faintest sign of their wrinkled parent. They looked exactly as if 

 both parents had sprung from rounded seeds. The interesting fact turned up, 

 however, that when he planted these seeds of double parentage, they behaved 

 very differently. The vines growing from them produced vines bearing chiefly 

 round peas. A small portion of them, however, came out wrinkled. From 

 this it was evident to Mendel that these hybrid yellow peas, which had one 

 round ancestor and one wrinkled ancestor, could carry, under their seeming 

 smoothness, the power of sometimes reproducing their wrinkled ancestor. 

 Now Mendel began to cross smooth and wrinkled peas and to replant every 

 pea produced by them, keeping an accurate record of the exact number of and 

 pedigree of each sort of seed produced. When he did this, he found that the 

 round and wrinkled peas were always produced in practically the same propor- 

 tion, that is, of three to one. One can realize how carefully this work was done 

 when we find that in studying the form of these seeds his record for round and 

 wrinkled shows that he had 5474 round peas to 1850 wrinkled peas. This is 

 in the ratio of 2.96 to i. A little later another experiment with yellow and 

 with green peas gave him 6022 yellow peas to 2001 green. This is in the ratio 

 of 3.01 to I. It becomes evident here that the law, to which accident 

 naturally will make exceptions, is that these forms will be produced in the 

 ratio of three to one. Accordingly, whenever he crossed round and wrinkled 

 peas, the product in the first generation always consisted entirely of round 

 peas, but these peas replanted produced in the next generation peas three- 

 fourths of which were round and one-fourth wrinkled. These results were 

 repeated so often that there could be no possibility that this figure was a mere 

 accident. 



Even this was not the end. As has been mentioned, this second genera- 

 tion had three times as many round as wrinkled. Mendel soon found that not 

 all these three round peas were aHke. When planted again, self-fertiHzed, one- 



