28 . ' EXPEEIMENT STATION RECORD, 



or among tbeuiselves. Seedlings of tlie common cultivated potato are known 

 10 differ widely. A study of the pollen grains showed uniformity iu all the 

 wild species in that they were pi-actically all oval or elliptical, whereas the 

 pollen grains of the cultivated potato are irregular in form and size. 



The studies with /S. ctuberosum are reported at some length, and it appears 

 that on account of the resistance of this species to potato blight it may be of 

 economic value. This species was grown continuously for more than 20 years, 

 during which time no variation was observed either in foliage or flowers. In 

 190G one seed pod developed and ripened, from which 20 young plants were 

 raised. These exhibited the same variation that is met with among the seed- 

 lings of the cultivated potato. Later a number of flowers were artificially 

 pollinated, and the seedlings raised in 190S exhibited the same variability in 

 character of foliage, color of flowers, etc. 



From the uniform character and shape of the pollen grain and other charac- 

 teristics, the author believes that S. etubcrosum is a primitive specific form, 

 and that the great variability of its seedlings points to the conclusion that this 

 may probably be the parent form of the cultivated potato. 



Breeding strains of plants, C. B. Davenport {Corncgic Inst. Waxlihn/ton 

 Year Book, 7 {1908), pp. 92-96). — A progress report is given of the studies of 

 Dr. G. H. Shull on breeding strains of ))lants, the lines of investigation including 

 a large number of species, among them beans, maize, sunflowers, poppies. Lych- 

 nis, Verbascum, etc. 



Among the more important results from an agricultural standpoint are those 

 obtained with maize. During the season covered by the report 38 pedigreed 

 strains of maize represented by about G,.500 individuals were examined, and it 

 is stated that — 



" Studies on the effects of cross- and self-fertilization in maize have given 

 further evidence that an ordinary field of Indian corn consists of a series of 

 more or less complex hybrids among numerous elementary species or biotypes, 

 and that the apparently injurious effects of self-fertilization .are due simply 

 to the unfavorable comparison of pure strains with their hybrids, and of less 

 complex hybrids with more complex ones. Self-fertilization sooner or later 

 reduces any pedigree to the condition of a pure strain by eliminating its hybrid 

 elements. According to this hypothesis, wlien the strain is once reduced to a 

 pure state, no further deterioration should result from continued self-fertiliza- 

 tion. All the evidences available at this time appear to support this propo- 

 sition." 



Brief accounts are appended on the studies of Dr. J. A. Harris on variation 

 and correlation in wild plants, and of Miss Anne M. liUtz's cell studies iu 

 heredity. 



The superiority of line breeding' over narrow breeding, O. F. Cook ( U. 8. 

 Dept. Agr., Bur. Plant Indus. Bui. IJfG, pp. ^5). — The purpose of this paper is 

 to point out some of the sources of confusion which have interfered with defi- 

 nite scientific solutions of ])roblems of breeding and to indicate a point of view 

 from which contradictory opinions can be reconciled. 



The author recognizes three forms of breeding, broad breeding, which is the 

 condition of descent found iu natural species and involves a free "interbreeding 

 of a large number of individuals, resulting in many lines of descent; narrow 

 breeding, which is the condition of descent found in carefully selected varieties 

 and embraces relatively small numbers of closely similar individuals; and line 

 breeding, which is the condition of descent of strains descended from single 

 individuals propagated without interbreeding with other lines of descent. Line 

 breeding includes in-and-in breeding, self-fertilization, parthenogensis. and vege- 

 tative propagation. The different types of breeding are discussed at some 

 length, and the superiority of line breeding iu fixing characters is pointed out. 



