MUTATIONS IN PLANT BREEDING 367 



varieties grown in this country in 1895 had a similar origin. There is no 

 reason to suppose the number has decreased and it is probably larger. 

 There is good evidence (see Chapter XIV) to show that bud sports arise 

 through factor mutations and that they occur in as great diversity as do 

 seed sports. Sometimes striking morphological or substantive changes 

 are produced but probably the somatic effect is often slight and hence 

 not easily detected (Chapter XXIII). 



Mutations in Crop Plants. Johannsen has reported two mutations 

 in his pure lines of beans. The careful statistical analysis of his successive 

 pure line families revealed the first mutant in 1903 and Johannsen thinks 

 it appeared as a bud sport. It was characterized by its large size and 

 relatively narrow shape. As it was constant from the first it must have 

 originated in homozygous condition. The second mutant bore seeds 

 which were relatively broad in shape. It could be traced back to 1907 

 when it existed in heterozygous condition. Later it was obtained in pure 

 line. Very recently mutations of great commercial value occurred in the 

 Florida Velvet Bean, Stizolobium deeringianum. The old variety was 

 limited to Florida and the Gulf Coast on account of lateness. About 

 1,000,000 acres were grown in 1915. We are informed by Piper that early 

 varieties originated by mutation at at least three different places, the first 

 in 1906. These resulted in the crop being adapted to the entire cotton 

 belt and in a very rapid increase in acreage since 1915. In 1916 about 

 2,650,000 acres were grown and in 1917, about 6,000,000 acres. 



Hayes describes a number of mutations in tobacco which is normally 

 self-fertilized. The first was found in a homozygous strain of the 

 Connecticut Cuban shade variety of commercial tobacco (N. tabacum). 

 This strain bears from 14 to 25 leaves per plant, the mean number 

 for 1910 and again for 1914 being 19.9 leaves. In 1912 the Windsor 

 Tobacco Growers Corporation grew about 100 acres of this strain 

 and during the clearing of the field three^ plants were found that had 

 not yet bloomed and which bore a number of uncut leaves. One of 

 these was transplanted to the greenhouse of the Connecticut Agri- 

 cultural Experiment Station. It produced 72 leaves on the main stem 

 and blossomed about January first. All the seedlings grown from this 

 plant came true to the new type which differs from the parent strain 

 "in having leaves of a somewhat lighter green shade, in a partial absence 

 of basal suckers, and in a practically indeterminate growth " (see Fig. 150) . 

 The quality of leaf seems as good as the Cuban and an increased yield 

 per acre of approximately 90 per cent, has been obtained, but it is yet 

 too soon to know how satisfactorily the new variety will conform to 

 trade requirements. Several similar mutants have been found in plan- 

 tations of the Connecticut Havana variety. This variety has been 

 grown in Connecticut for over 50 years and is uniform in habit of growth. 



