82 Heredity and Environment 



in the Proceedings of the Natural History Society of Briinn in 

 1866. The paper attracted but little attention at the time al- 

 though it contained some of the most important discoveries re- 

 garding inheritance which had ever been made, and it remained 

 buried and practically unknown for thirty-five years. Plant hy- 

 bridization had been studied extensively before Mendel began hid 

 work, but he carried on his observations of the hybrids and of 

 their progeny for a longer time and with greater analytical ability 

 than any previous investigator had done. The methods and re- 

 sults of his work are so well known through the writings of Bate- 

 son, Punnett, and many others that it is unnecessary to dwell at 

 length upon them here. In brief Mendel's method consisted in 

 crossing two forms having distinct characters, and then in count- 

 ing the number of offspring in successive generations showing one 

 or the other of these characters. 



Mendel's Experiments on Peas. — During the eight years pre- 

 ceding the publication of his paper in 1866 Mendel hybridized 

 some twenty-two varieties of garden peas. This group of plants 

 was chosen because the different varieties could be cross-fertilized 

 or self-fertilized and were easily protected from the influence of 

 foreign pollen ; because the hybrids and their offspring remained 

 fertile through successive generations ; and because the different 

 varieties are distinguished by constant differentiating characters. 

 Mendel devoted his attention to seven of these characters, which 

 he followed through several generations of hybrids, viz., 



(1) Differences in the form of the ripe seeds, whether round or 

 wrinkled. 



(2) Differences in the color of the food material within the 

 seeds, Avhether pale yellow, orange or green. 



(3) Differences in the color of the seed coats (and in some 

 cases of the flowers also), whether white, gray, gray brown, 

 leather brown, with or without violet spots. 



(4) Differences in the form of the ripe pods, whether simply 

 inflated or constricted between the seeds. 



