CHAPTER XL 



OTHER THEORIES OF SPECIES-FORMING AND 

 DESCENT ( CONTINUED ) : ALTERNATIVE 

 THEORIES (CONTINUED). 



Heter agenesis. Under the name heterogenesis we have 

 to consider a theory of species-forming which is more popu- 

 larly and widely known under another name, viz., the muta- 

 tions theory. This theory is commonly associated with the 

 name of de Vries, the Amsterdam botanist. But this gen- 

 eral conception of species-forming on a basis of the occur- 

 rence of occasional, sudden, fixed, and often considerable 

 changes or variations in the offspring of a plant or animal, 

 is a conception not of course new with de Vries, but one 

 variously expressed by numerous biologists from Dar- 

 win's time on, especially by von Kolliker, Galton, Dall, 

 Bateson, Emery, Scott, and Korschinsky. It is, however, 

 chiefly due to the patient, persistent, well-planned, and ex- 

 tensive experiments and observations of de Vries that this 

 theory of species-forming by heterogenesis, or as called by 

 de Vries, by mutations, has recently received so much re- 

 newed attention. With the observations of de Vries on the 

 breeding of certain plant species, notably certain CE'notheras 

 (evening primroses), there have been much associated in 

 recent popular scientific literature accounts of the ear- 

 lier observations of Gregor Mendel, 1 an Augustinian monk, 

 who recorded, in 1865, in an obscure journal, some very 

 valuable observations and logical conclusions concerning the 

 phenomena of heredity in certain other plants (especially 

 .garden peas). Reference should also be made, in this con- 



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