268 BIOLOGY: GENERAL AND MEDICAL 



ability to recognize the Mendelian characters that has 

 made it possible to formulate a law as to their mode of 

 transmission. 



Mendel worked with peas because the sexual organs of 

 these flowers are enclosed by the petals in such manner 

 that self-fertilization is inevitable. To make the hybrids, 

 he had to cut away part of the flower, remove the unripe 

 anthers, and at the time of the maturation of the stigma 

 apply such pollen as was desired. 



It was soon discovered that certain characters of 

 the peas were traceable from generation to generation, 

 appearing in recognizable form in the normal individual 

 and in the hybrid. Such characters are, for example, 

 color of the flower, size of the plant, quantity of sugar 

 in the seed, and quantity of starch in the seed. These 

 characters which appear to blend with their opposites in 

 the hybrids of the first generation are found by an 

 examination of the second generation to have effected 

 a temporary combination which loosens up and begins 

 to separate, so that with each succeeding generation a 

 greater number of the offspring revert to the parental 

 types until after, say, ten generations scarcely any hybrid 

 organisms remain. 



These facts were in thorough accord with well-known 

 facts concerning flowers. Many of our most beautiful 

 garden flowers are hybrids, some of which were produced 

 only after infinite pains had been taken in their cultiva- 

 tion. If they are fertile and "go to seed," everyone 

 that has enjoyed a garden knows with what dismay 

 he views the plants growing from the hybrid seeds which 

 yield a few of the desired forms among a large number 

 of simple and commonplace flowers. Though this fact 

 was known in Mendel's time, and it was generally con- 

 ceded that hybrids "tended to revert to the primitive 

 types," he alone had the genius to follow the matter with 

 scientific accuracy, to reduce the reversion to a mathe- 

 matical basis, and to lay the foundation of a new 

 principle of much importance in studying the problems 

 of heredity. 



