MUTATION IN EGYPTIAN COTTON 
By Thomas H. Kearney, 
Physiologist in Charge , Alkali and Drought Resistant Plant Investigations, 
Bureau of Plant Industry 
INTRODUCTION 
The occurrence of saltatory or discontinuous variations has frequently 
been reported by breeders of plants. Most of the instances mentioned 
in the older literature were not supported by unimpeachable evidence, 
but in the aggregate they established a strong presumption of the reality 
of this type of variation. Recent investigation has led to a better under¬ 
standing of the phenomenon, which is now generally known as mutation. 1 
The publication of De Vries's work “Die Mutationstheorie” (1901- 
1903) 2 focused the attention of biologists upon the phenomenon of muta¬ 
tion by suggesting that it is not confined to domesticated organisms, 
but is also met with among wild species, and that organic evolution has 
taken place through the natural selection of mutations rather than of 
minor variations. While De Vries's theory of evolution has not won 
general acceptance, great interest attaches to his discovery of a plant in 
which mutation is a frequent rather than an extremely rare occurrence 
and from which numerous distinct and regularly heritable forms capable 
of description as elementary species or biotypes have been thus derived 
during a short period of time. 
Among seed-propagated crop plants 3 there have been few well- 
substantiated instances of the origin by mutation of varieties which differ 
in several characters from the parental type, although their apparent 
rarity is perhaps attributable to imperfect knowledge of the history of 
1 Mutation in plants may be defined as a type of variation manifesting itself in the sudden appearance 
of a distinctly different individual the characters of which are uniformly expressed by its descendants 
when self-pollinated or cross-pollinated only among themselves. 
This definition, which applies only to the higher plants, is purposely worded so as to exclude reference 
to the cause of mutation and to the conditions under which it takes place. Johannsen (1913, p. 161) has de¬ 
fined mutation as a sudden, discontinuous alteration of the biotype, independent of all crossing. This limi¬ 
tation of the term seems ill-advised, because it leaves us without a designation for the well-known cases 
which most biologists regard as the best examples of mutation and which represent a distinct and im¬ 
portant phenomenon, although probably to be interpreted as resulting from remote or complex hybridiza¬ 
tion. 
2 Bibliographic citations in parentheses refer to ‘‘literature cited,” p. 301. 
8 “It must not be forgotten that the agricultural improved races do not possess the constancy of true 
species; whereas the varieties and subspecies of the horticulturist can only be distinguished from true 
species historically and systematically—not experimentally * * * In horticulture varieties arise by 
mutations, and varieties are elementary species. In agriculture, according to the current view and except¬ 
ing in the instances of the unconscious isolation of elementary species, the highly improved races arise 
gradually through selection, but they never become species.” (De Vries, 1909, v. 1, p. 82.) 
Journal of Agricultural Research, 
Dept, of Agriculture, Washington, D. C. 
(287) 
Vol. II, No. 4 
July 15, 1914 
O-26 
