SEEDS AND SEEDLINGS 83 



seem to come from hybridizing. Of recent years new theories have 

 been advanced accounting for the variation and heredity of plants 

 and animals. One, by a Dutchman named Hugo de Vries, is 

 that new species of plants and animals arise suddenly by " muta- 

 tions " or steps. This means that new species instead of arising 

 from very slight variations, continuing during long periods of years 

 (as Darwin believed), might arise very suddenly as a very great 

 variation which would at once breed true. It is easily seen that 

 such a condition would be of immense value to breeders, as new 

 plants or animals quite unlike their parents might thus be formed 

 and perpetuated. It will be the future problem of plant breeders 

 to isolate and breed " mutants," as such plants are called. 1 



' 



REFERENCE BOOKS 





 '.- 



ELEMENTARY 



Sharpe, A Laboratory Manual for the Solution of Problems in Biology. American 



Book Company. 



Andrews, Botany all the Year Round, pages 103-119. American Book Company. 

 Atkinson, First Studies of Plant Life, Chaps. I, II, III, XXV. Ginn and Company. 

 Cornell Nature Study Leaflets, XXVIII, XLII, XLIV. N.Y. Department of 



Agriculture. 



Dana, Plants and their Children, pages 50-98. American Book Company. 

 Harwood, New Creations in Plant Life. The Macmillan Company. 



ADVANCED 



Coulter, Barnes, and Cowles, A Textbook of Botany, Part II. American Book Com- 

 pany. 



De Candolle, Origin of Cultivated Plants. D. Appleton and Company. 



De Vries, Species and Varieties, edited by D. T. MacDougal. Open Court Pub- 

 lishing Company. 



Farmers' Bulletin, 229. 



Goodale, Physiological Botany. American Book Company. 



MacDougal, Plant Physiology. Longmans, Green, and Company. 



Punnett, R. C., Mendelism. Cambridge, England. 



Thompson, Heredity. John Murray, London. 



University of Illinois Agricultural Station, Bulletin 87. 



University of Minnesota Agricultural Station, Bulletin 165. 



Wallace, Darwinism. The Macmillan Company. 



Yearbook, U.S. Department of Agriculture. 



1 The part played by Mendel's law is too difficult to explain to high-school pupils. 

 For a well-organized statement of recent work, see Bailey's Plant Breeding or 

 "The Relation of Certain Biological Principles to Plant Breeding " E. M. East, 

 Bulletin 158, Conn. Agri. Exp. Station, New Haven, Conn. 



