No. 638] 



TYPES OF MUTATIOX! 



263 



present conceptions of them as are mutations in the 

 Oenotheras from the conceptions in tk^^ries's chissical 

 publication, "The Mutation Theory." It may still he 

 desirable to employ the word mnidiion as a collective 

 term to designate the sudden appearance (<f aii> a])i>arciit 

 genetic novelty— whatever its real cause -until \vt' kiu)W 

 better. Strictly speaking 1 sliouhl not call clii-omosomal 

 aberraticjis mutation.- when the changes are purely quan- 

 titative. The occurrence of telraploidy would therefore 

 be no more a mutation tlian the doul)ling of chromosomes 

 at the origin of the sporopliyte from the gametophyte of 

 ferns. 



We have seen that chromosomal duplications and re- 

 lated phenomena may simulate gene mutations in their 

 effects upon the individual. What is their possible sig- 

 nificance in evolution? Let us first consider tetraploidy. 

 Numerous investigators have called attention to the fact 

 that the chromosome numbers of plants ai'e mow fre- 

 quently in multiples of two and four than om- would ex- 

 pect from random sampling. Pairs of related species 

 have been listed for which one member had twice a>- many 



called tetra])hud. We feel stnm-ly tln^ drsirability of 

 confining the term tet raj )loid\- to tho>e ca-es in which the 

 4x number is brought about by a doubling of homologous 

 chromosomes. Doul)ling by trans\-ei'>e di\ isiou is a pos- 

 sible method, but would not l)e iiududed in the term. 



Tetraploidy has l)een ol)ser\ ed in experimental cultures 

 of oMiothera, i)rimula and datura. Do such tetraploid 

 plants occur in natur(^ and are \\\vy ca])al.le of giving 

 rise to tax(Uiomicaliy new -pedes .' It may he mentioned 

 that the tetraploid datura was called Xew Species " be- 



slight chance (^f lieing swamped by hy]»ridization with the 



