146 DOCTRINE OF EVOLUTION 



was propounded by Gregor Mendel on the basis of 

 extensive experiments upon plants conducted during 

 many years, 1860 and later, in the obscurity of his 

 monastery garden at Altbriinn, in Austria. It was 

 rescued from oblivion by De Vries, who found it buried 

 in a mass of literature and brought it to light when he 

 published his renowned Mutation Theory in 1901. 

 Mendelian phenomena of inheritance, confirmed and 

 extended by numerous workers with plants and ani- 

 mals, prove that in many cases portions of the streams 

 of germ plasm that combine to form the hereditary 

 content of organisms may retain their individuality 

 during embryonic and later development, and that they 

 may emerge in their original purity when the germ-cells 

 destined to form a later generation undergo the pre- 

 paratory processes of maturation. They demonstrate 

 also the apparent chance nature of the phenomena of 

 inheritance. To my mind the most striking and sig- 

 nificant result in this field is the demonstration that a 

 particular chromosome or chromatin mass determines 

 a particular character of an adult organism, which is 

 quite a different matter from the reference of all the 

 hereditary characters to the chromatin as a whole. 

 Wilson and others have brought forward convincing 

 proof that the complex character of sex in insects 

 actually resides in or is determined by particular and 

 definite masses of this wonderful physical basis of 

 inheritance. 



Mendel's principles also account in the most remark- 

 able way for many previously obscure phenomena, 

 like reversion, or a case where a child resembles its 

 grandparent more than it does either of its parents; 



