HEREDITY 187 



many individuals showing many simultaneous, usually slight 

 but real differences from the parents in various parts and func- 

 tions. These are the differences called mutations by de Vries 

 and his followers, and are the basis of the at present consid- 

 erably accepted theory of species-forming by heterogenesis or 

 sudden complete fixed modifications of organic types. In the 

 light of the observations and experiments of de Vries, these mu- 

 tations are of special importance in any consideration of hered- 

 ity and variation. (See p. 157, Chapter IX, for a brief account 

 of these mutations.) 



The Mendelian "laws" apply only, probably, to certain par- 

 ticular categories of inheritance, or rather categories of char- 

 acters. That is, so far as worked out, the Mendelian principles 

 seem to have definite application only to cases of inheritance in 

 which the characteristics under observation are mutually ex- 

 clusive or alternative in character; categories (1) and (3) in 

 our list in a preceding paragraph are the only ones under the 

 rule of the Mendelian principles, and there are even some ex- 

 ceptions in these categories. The various other kinds of inher- 

 itance, called blended or combined (where the two characteristics 

 fuse or blend to form a new condition) , and mosaic or par- 

 ticulate (where both parental characteristics exist side by side 

 in each individual among the young), apparently require for 

 their explanation something besides the Mendelian principle. 



At some time between 1855 and 1865 Gregor Johann Mendel, 

 an Augustinian monk in the small Austrian village of Brimn, 

 carried on in the gardens of his cloister pedigree cultures of peas 

 and some other plants from which he derived data which he read, 

 together with his interpretation of their significance, before 

 meetings of the Natural History Society of Briinn, and which 

 in the same year of their reading (1865) were published under the 

 title "Experiments in Plant-hybridization," in the Abhand- 

 lungen (vol. iv), of the society. Mendel was the son of a peas- 

 ant, and had been educated in Augustinian foundations and 

 ordained a priest. For two or three years he studied physics 

 and natural science in Vienna, and refers to himself in one of his 

 papers as a student of Kollar. He became abbot of his cloister, 

 and was for a time president of the Briinn Natural History 

 Society. Such are the essential details of the education and 

 work of the man whose name will undoubtedly live forever in 

 the annals of biological science. 



