[REPRODUCTION AND HEEEDITY 315 



that we get in all twelve equal pairs. It is possible to prove 

 that of each of these chromosome-pairs one part is of maternal, 

 the other of paternal origin. We have already assumed that the 

 paternal nuclear loops which became united by fertilization 

 become once more separated during the course of the maturing 

 of the ovum. In this case, owing to the different appearance 

 of the chromosomes the process may be directly observed, for 

 of each pair of nuclear loops only one reaches, during division, 

 the nucleus of the semen-forming cell. 



Apart from the investigations of the cells and observations 

 of the processes of fertilization, there is another way which 

 leads us into the mysterious region of heredity : rational breeding 

 experiments. Both ways lead towards the same goal, and if 

 they meet or run parallel, if only for short distances, we can 

 see in that fact a proof that we are on the track of truth. 



Half a century ago this second path was chosen by Mendel, 

 an Augustinian priest, in the Queen's cloister at Briinn. Earely 

 has a great success met with a stranger fate. Buried in a 

 little unknown journal, the record of these remarkable ex- 

 periments slept unnoticed and forgotten, until in the first year 

 of this century the facts which they proved were re-discovered 

 independently and almost simultaneously by three investigators, 

 de Vries, Correns, and Tschermak, and confirmed by new com- 

 prehensive experiments. As Correns justly remarked, this 

 long period of oblivion was a heavy loss to science, but fortu- 

 nate for Mendel's posthumous fame, ' for if his work had 

 been immediately understood we should not now speak of 

 4 Mendel's law ' and ' Mendelism.' The rapid advance of science 

 would have soon overtaken the labours of this solitary man and 

 left them far behind. 



For his important experiments Mendel employed chiefly peas. 

 From seed merchants he bought thirty-four varieties of peas 

 which differed in various characteristics : the shape of the mature 

 seed, the position of the leaves, the colour of the seeds, etc. By 

 cultivating each kind for two years he determined whether the 

 character of each variety remained constant, and then chose for 

 his experiments only those which had stood the test successfully. 

 For many years Mendel continued his experiments, and only after 

 having made more than ten thousand ' crosses ' did he decide 



