CHAPTER XIV 



The Mendelian experiments in hybridization The doctrine of unit 

 characters and the purity of the gametes Galton's law of inheritance. 



WHATEVER view we may adopt as to the mechanism of heredity 

 there can be no doubt as to the existence of a material foundation 

 for the transmission of characters from parent to offspring. We 

 know that the protoplasm which forms the material basis of all 

 living things is continuous, by means of the germ cells or gametes, 

 in an unbroken stream from one generation to another. At each 

 conjugation of gametes, however, two such streams are mingled, 

 and the offspring receives part of its initial stock of protoplasm 

 from one parent and part from the other, each part bringing with 

 it all the potentialities which may have been derived from a long 

 line of ancestors. Bearing these facts in mind, we must now 

 direct our attention to some results which have been obtained 

 by the "Mendelian" method of attacking the problem of 

 heredity. 



In the early part of the nineteenth century much attention was 

 paid by horticulturists to experiments on the hybridization of 

 plants. It was found that, within certain limits, it was possible 

 to fertilize the flower of one variety of plant with the pollen 

 of another variety, and in this manner to alter the character 

 of the offspring. Many .crosses or hybrids between different 

 varieties were thus obtained, differing in various ways from 

 the parent plants. It was also found that by repeatedly fertilizing 

 the flowers of one variety with the pollen of another the 

 descendants of the first could be entirely changed into the second. 

 This clearly proved that all the distinctive characters of the male 

 parent were in some way represented in the pollen grains, and 

 could be transmitted by these to future generations, but it also 

 proved something more, it proved that it was possible to 

 eliminate the special characters of the female parent, or at least 

 to prevent them from manifesting themselves in the offspring. 



As a rule it is only possible to bring such experiments to a 



