cries, and of the formulation of Mendel's Law and of 

 De Vries' Mutation Theory. The first-named law was pro- 

 pounded by Gregor Mendel on the basis of extensive ex- 

 periments upon plants conducted during many years, 

 from 1860 on, in the obscurity of his monastery garden at 

 Altbriinn, in Germany. 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 Muta- 

 tion Theory in 1901. Mendelian phenomena of inheri- 

 tance, confirmed and extended by numerous workers with 

 plants and animals, prove that in many cases portions of 

 streams of germ-plasm that combine to form the hered- 

 itary 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 prepara- 

 tory processes called maturation. They demonstrate also 

 the apparent chance nature of the phenomena of inheri- 

 tance. I think the most striking and significant result in 

 this field is the proof that a particular chromosome or chro- 

 matin mass determines a particular character of an adult 

 organism, which is quite a different matter from the 

 reference of all the hereditary characters to all of the 

 chromatin. Professor Wilson has brought forward the 

 convincing data showing that the complex character of sex 

 in insects actually resides in or is determined by particular 

 and definite masses of this wonderful basis of inheritance. 

 Mendel's principles also account in the most remarka- 

 ble way for many previously obscure phenomena, such as 

 reversion, and again, the case where a child resembles its 

 grandparent more than either of its parents; these seem 

 to be due, so to speak, to the rise to the surface of a hidden 

 stream of germ-plasm that had flowed for one or many 

 generations beneath its accompanying currents. I believe 

 that the law is replacing more and more the laws of Gal- 



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