HEREDITY 187 



many individuals showing man}' simultaneous, usualh' sli^^ht 

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

 tions. These are the differences called mutations by de Vries 

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

 jrrbly accepted theory of species-forming by heterogenesis or 

 sudden comj^lete fixed modifications of organic types. In tlie 

 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, Chai)ter IX, for a brief account 

 of these mutations.) 



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

 ticular categories of inheritance, or rather categories of char- 

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

 seem to have definite application only to cases of inheritance in 

 which the characteristics under observation are nuitually ex- 

 clusive or alternative in character; categories (1) and (:5) 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 (wiiere both parental characteristics exist side by side 

 in each individual among the young), a])parently recpiire for 

 their explanation something besides the ]\Iendehan principle. 



At some time between 1855 and 1865 Gregor Johann Mendel, 

 an Augustinian monk in the small Austrian village of Briinn, 

 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, !)efore 

 meetings of the Natural History vSociety of Briinn, and wiiich 

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

 title " ExpcM'iments in Plant-hybridization," in tlie Ahhand- 

 lungen (vol. iv), of the society. Mendel was the son of a jn^as- 

 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 becanu' abbot of his cloister, 

 and was for a time president of tlie Briinn Natural History 

 Society. Such are the essential details of the education and 

 work of the man whose name will undoubtedly live forevor fu 

 the annals of biological science. 



