288 
Journal of Agricultural Research 
Vol. II, No. 4 
varieties in these groups. 1 Evidence is presented in this paper which is 
believed to justify the conclusion that mutation occurs in Egyptian 
cotton and that numerous varieties have thus arisen in Egypt and in 
Arizona. 
Many biologists hold that mutation as observed by De Vries is an 
after-effect of hybridization. The mutability of Egyptian cotton is capa¬ 
ble of a similar explanation, for it is widely believed that the type as a 
whole originated as a hybrid. It can at least be shown that the varieties 
now grown in Egypt, including the one which has given rise to the Ari¬ 
zona varieties, have been constantly exposed to crossing among themselves 
and with other types of cotton. 
The breeder who works with a mutable group of plants has a great 
advantage in the ease with which new varieties can be fixed. It has 
been possible to maintain a high degree of uniformity in the varieties 
of Egyptian cotton which have arisen in Arizona by keeping each new 
form isolated from other types of cotton and by removing the relatively 
few aberrant plants from the seed increase fields before they come into 
blossom. In Egypt the maintenance of the cotton industry has largely 
depended upon the successive appearance of desirable mutants, since 
until very recently no adequate measures were taken to preserve a pure 
seed supply and each new variety rapidly deteriorated as a result of 
cross-pollination. While under the Arizona conditions deterioration is 
likely to be less rapid, the tendency of this type of cotton to produce an 
occasional valuable mutant may be regarded as a form of insurance 
against the possible “running out” of the present varieties. 
The subjects treated in the following pages are: (i) The origin of 
Egyptian cotton, so far as it throws light upon the heterogeneous 
nature of this type and thus affords a possible explanation of its muta¬ 
bility; (2) the evidence for the mutational origin of the several varieties 
now grown commercially in Egypt; (3) the better known history of 
the Arizona varieties and the reasons for concluding that they have 
arisen by mutation, and (4) the evidence afforded by Egyptian cotton 
that mutability may be a result of hybridization. 
The photographs used in illustrating this paper were made by Messrs. 
C. B. Doyle and Bruce Gilbert, of the Office of Acclimatization and 
Adaptation of Crop Plants and Cotton Breeding, Bureau of Plant 
Industry. 
1 There is some evidence that mutation occurs in tobacco. Mr. A. I). Shame! believes that the “Halli- 
day ” variety originated in this manner, although East and Hayes (1914) claim to have obtained an iden¬ 
tical form in the Fa of a SumatraX Havana cross and consider it to represent merely a Mendelian recom¬ 
bination of the characters of the parent types. On the other hand, these authors (1914. P- 45) state that in 
tobacco "mutations may occur. We have shown the origin of one family by a very wide mutation. In 
this particular case it was not difficult to show that a constitutional change took place in a single germ 
cell of the mother plant." 
A presumable case of mutation in barley has recently been described by L. Kiessling (1912). 
