146^ 



THE AGRICULTURAL SEWS. 



MA^Tl.^■^ la^/ 



DOES MUTATION OCCUR IN 

 GOSSYPIUM? 



An interesting paprr by Thomas H Kearney, enmled 

 'A Plant Industry Based on Mutation" appears in the 

 Joiiriuil ,i/Jhii\iit\ior February 1918 Accotfling to the 

 author, experiments to determine whether Egyptian cotton 

 coold be grown in ihe Inited States were begun by the 

 United States Department of Agriculture some twenty years 

 ago. 



Several introductions were made, the most important 

 being by Mr. David Fairchild, who vi.sited Kgypt in 1 899. 

 and obtained seed of the principal varieties then grown in 

 that country. This seed was tested by Dr. H. .J. Webber 

 at a number of stations in the southern and .south-eastern 

 States. All the varieties, when first introduced, were not 

 only relatively late in ripening, and unfruitful, but were 

 extremely variable. I'lant breeding experiments were begun 

 by Mr. Kearney at N uma, Arizona, in 1903, with the variety 

 Mit Atifi. Selection was carried on for several years, result- 

 ing in a gradual improvenienl in the uniformity, earline,ss 

 an<i productivity, in the manner in which the bolls opened, 

 and in length of the tibre. Up to this point no maiked 

 change of type was observed to have taken place. 



A new era in the breeding work began in 1 908, when 

 two of the progeny rows were found to differ strikingly 

 from the parent stock, and from one another. These rows 

 gave rise to the Yuma and Somerton varieties. The Yuma 

 variety was pre.served, and became the basis of the Egyptian 

 cotton industry in Arizona. This vjiriety differed from the 

 parent Mit Afifi in numerous characters, of which the most 

 ■ onspicuous were the longer (about U inches) and lighter- 

 coloured fibre. Another variety, the Pima, was derived 

 from Mit Afifi through 'Suiua. In 1910, in a field of \ uma 

 cotton at Saccaton, .\rizona, a plant was selected because 

 of its superior productiveness and length of fibre. Upon 

 examination of the remarkably uniform progeny row which 

 was grown the following year from seed produced by I his plant, 

 it was evident that another new and very distinct variety 

 had appeared. As compared with the parent variety (N'uma), 

 Pima is distinguished by its fewer vegetative branches and 

 better developed fruiting branches, by its plumper, more 

 sharply pointed, and less deeply pitted bolls, and by its 

 longer (lit"!! imhes), finer, silkier, and lighter-coloured 

 fibre. 



The commercial production of Egyptian cotton in 

 Arizona began in 1912, i.e., some thirteen year.s after the 

 original experiments were initiated. In that year the 

 United States Department of Agriculture .supplied seed of 

 the ^'uma variety to planters in the Salt Hiver \alley, and 

 some 200 acies were planted. 



From this .small beginning the industry expanded, until 

 in 1917. in the Salt Hiver Valley alone, about 2:!.0OO acres 

 of Vuma cotton and about 7,000 aires of I'ima cotton were 

 grown, and the value to the farmers of the llbro and see<l 

 produced wa.s e.stimated at about §.j,O00,00O. The prospects 

 are that in 1918 not less than 100.000 acres will b<- planted 

 to this crop. 



The fibre of both the ^ uiua and I'ima varieties has 

 found much favour with .\merican spinners, the automobile 

 tire manufacturers having shown especial interest in this 

 product. 



Here then, in brief, is the history of the development 

 of the Egyptian cotton icdu.stry in the south western 

 United States. No one will grudge unstinted praise to the 

 patient invfstigators who have built up such a flourishing 



industry, least of all «(0y one familiar with the great dijtir. 

 cultics inherent in cotton breeding work. .-,,- 



But in the article under discussion, and in a former 

 paper, \'r. Kearney has definitely committed himself to the 

 view that the varieties Yuma iind Pima have been developed 

 from Mit Afifi by mutational origin, and it is up m his 

 scientific opinions, and not on the econoniic results which 

 have developed out of the work of himself and his associates, 

 tint the pre-^ent writer wishes to oti'er some criticism- 

 First of all, what does Mr. Kearney mean by the term 

 mutation! His own definition is as as follows: 'Mutation 

 in [ilauts may be defined as a type of variation manifesting 

 itself in the sudden appearance of a di>tinctly ditl'erent 

 individual, the charactets of which are uniformly expressed 

 by its descendants when self-pollinated or cross-poliinat-d 

 among themselve.s.' The meaning which we must attach to 

 tliis statement is that a homozygous individual suddenly 

 appears in (a) a mixture of honiozygote-s and lieterozyg ot'-s, 

 (b) a population of heterozygotes only, or (c) a population of 

 homozygotes only. 



Mr. Kearney rejects Johannsens definition of mutation 

 as a sudden discontinuous alteration of the biotype, indepen- 

 dent of all crossing, because such a limitation of the term 

 leaves us without a de.sij!natiin for the well-known cases 

 which most biologists regard as the best examples of muta- 

 tion, and which represent a distinct and important 

 phenomenon, although probably to be interpreted as 

 resulting from remote or comple.v hybridization. 



Later, Mr. Kearney states that mutation manifests 

 itself in the sudden appearance of au individual which diti'ers 

 from the parent stock in d/ic m- more strongly hcri:<}:'h 

 iharnctcn:. 'If this individual ''breeds true,' the new 

 characters being uniformly expressed in its progeny genera- 

 tion after generation, a stable variety will have been 

 produced.' 



.Vow if Mr. Kearney can show that the behaviour of his 

 new types of cotton conform to his first definition, he will 

 accomplish a fine piece of scientific work, but he has not yet 

 shown any such thing. He has expressed an opinion, but 

 he has not backed up that opinion by any ordered collection 

 of data which bear on it. 



Further, Mr. Kearneys first definition of mutation 

 seems to conflict with his .second, for it a|)pears that in 

 the latter he is not concerned whether the other characters 

 of the plant breed true or not. He only insists that the 

 plant must be homozygous for the 'new characters' How 

 many new characters would be sufficient for a Kearney 

 mutation! Would one be enough! If so, the appearance 

 of single-comb I'owls in F.j of a cross between ro.se and 

 pea-combed fowls would be a mutation, for it satisfies 

 Mr. Kearneys definition very well. 



Dr. Xilsson-J*;hle, at the Svalof Experiment Station, 

 crossed two red-kernelled sorts of wheat. The F, was red- 

 kernelled, but in the'V.j appeareil some white-kernelied 

 individuals which bred t,rue in I'' ,. .According to Mr. Kearney 

 this would be a mutation, although it was explained i|uite 

 simply by the hypothesis that each of the jjarents had its own 

 peculiar unit for red colour. The i-io.ss was of the nature 

 l!,r.; X r,!!... Thus ,'„ of the 1'.^ would be constant 

 r, r. (white). In general the appearance of a new constant 

 form ab in a cross a I! xAb— especially where ai{ and Ah 

 w>re outwardly alike — would be hailed as a mutation, 

 although such cases have been ex[)lained again and again 

 fjuite simply in .Men<Ielian terms. 



Agiiii, one is forced to ask for Mr. Kearney's evidence 

 as to th'' purity of his 'mutants'. So far as the [ire^ent 



