Il6 MAN, THE ANIMAL 



it is found that there is a rather fixed limit beyond 

 which each species does not vary. This limit is 

 not the same for all living things, being restricted 

 to minute changes in some and permitting marked 

 modifications in others. 



The ideas advanced by Mendel come nearer 

 to explaining this difficult phase of our subject 

 than the hypothesis of any one else, although it 

 should be said that the modern interpretations of 

 Mendel have carried his views much farther than 

 when he first formulated them. 



Johann Gregor Mendel, a monk of the monas- 

 tery of Briinn in Austria, spent eight years experi- 

 menting in his gardens with varieties of edible 

 peas. He carried on this work as a side issue and 

 for recreation. Up to the time that his observa- 

 tions were published in 1866, all writers upon 

 heredity had regarded the individual plant or ani- 

 mal as a unit. This meant that the hand char- 

 acters shown in Fig. 38 as well as all others were 

 bound up in an individual and could not be sorted 

 out. This important conception is made clearer 

 in the following experiment of Mendel's: 



He selected an edible pea that normally grew 

 six or seven feet tall and one that had a stem of 

 from one-half a foot to a foot and a half. When 

 these two varieties of peas were crossed (i.e., the 

 pollen of the short variety was placed on the 

 stigma of the tall variety or vice versa) the off- 



