or constant, species be established with no variation among individuals? Can 

 standard surroundings be established to prevent variation? What connection 

 is there between the characteristics of individuals and the structure of eggs 

 and sperms? 



Analyzing the Problem The first systematic experiments in heredity 

 of which we have any record were those of Gregor Mendel (1822-1884), an 

 Austrian monk. Mendel had long puzzled over the great amount of variation 

 among his garden peas. There were tall plants and short ones, plants with 

 white flowers and plants with colored flowers, with yellow seeds and with green 

 seeds, with smooth seeds and with wrinkled seeds. He noticed further that a 

 given plant might have any combination of the single members of these pairs. 

 Thus a hairy plant might be tall, or it might be short; a tall plant might have 

 white flowers or pink flowers; it might have yellow seeds or green seeds; and 

 so on. All in all, Mendel studied seven different pairs of contrasting charac- 

 teristics in the pea plants (see table, below). 



In one plot Mendel placed pollen from a tall plant upon the stigma of a 

 short, and vice versa. In another he crossed smooth-seeded and wrinkled- 

 seeded plants, in both directions. In this way Mendel made reciprocal crosses 

 with hundreds of pairs of plants having contrasting characters. 



Mendel's First Discovery- When Mendel crossed green-seed and yellow- 

 seed plants, the resulting seeds developed into plants yielding only yellow 

 seeds. When he crossed tall and dwarf plants, the offspring were all tall. 

 With each of his seven pairs of characters, Mendel found that the offspring 

 resembled one of the parents completely. Thus the offspring of colored -flower 

 and white-flower strains all had colored flowers. If these results are sur- 

 prising, it is because most of us have failed to notice that the resemblance 

 of children to their parents consists not only in having characters lying 



^Breeders long tried, without success, to find out how a hybrid "variety" acts in heredity. 

 Mendel crossed plants that differed from each other in a particular character — tallness, for example, 

 or color. In thousands of crossings between individuals with contrasting characters, he found that 

 all the hybrids in each series were alike, whether the quality in question had been carried by the 

 male parent or the female parent "See Nos. 1 and 2, p. 503. 



474 



