31 
Mutations and Evolution. 
CHAPTER II. 
Foundations of the Mutation Concept. 
In later chapters we shall deal with the occurrence of 
mutations in a wide range of wild plants and animals. 
The writer’s book on mutation 1 , dealt particularly with the 
mutations of CEnothera and the conclusions to be drawn from 
them. A cell theory of mutations was formulated, based on the 
cytological and breeding work with CEnothera and incidently a 
wide range of other forms; and concepts were developed which 
proved applicable to many other plants and animals. This has 
involved certain departures from the theory of mutations as 
originally propounded by de Vries. Instead of the purely 
hypothetical and conceptual pangens, whose alterations were the 
putative cause of mutations, it has been possible to link up many 
of the changes in CEnothera with visible structural changes in 
the chromatin of the cell. 
Let us consider for a moment the simplest case of this kind. 
It is already well-known, but requires restatement because some 
writers have endeavoured to deny the significance of the facts. 
The lata mutation is now known to occur in CE. lamarckiana , 
CE. biennis and CE. suaveolens. The peculiarities are the same in 
every case—obtuse-tipped, deeply crinkled leaves, a somewhat 
weak or irregular habit of growth, stout rounded buds, almost 
completely sterile anthers, and 15 chromosomes in the nuclei. This 
constellation of characters is super-imposed on, or rather substituted 
for, the characters of the species in each case, and the same 
mutation has also been observed from some of the mutants of 
CE. lamarckiana and also in various hybrids. Thus CE. biennis 
mut. lata has small flowers while CE. lamarckiana mut. lata has 
large flowers, but the lata forms otherwise agree. CE. lata 
rubricalyx, two of which occurred in the F 2 oi rubricalyx x grandijlora 
had lata peculiarities combined with the red pigmentation of 
rubricalyx. 2 It is also significant that lata mutants sometimes 
occur in pairs. 
Only one hypothesis based on observation has been suggested 
to account for the origin of lata with its 15 chromosomes. In 
1908 occasional irregular reduction divisions in the pollen 
mother cells were observed in CE. mut. rubrinervis whereby an 8-6 
separation of chromosomes took place in the heterotypic mitosis. 
This would lead to the formation of two pollen grains with 8 
* Gates, 1915. 7 Gates, 1914 ; Gates and Thomas, 1914. 
