HEREDITY AND VARIATION IN PLANTS 149 



Dr. Darrow and his coworkers at the Beltsville Md. Re- 

 search Center of the United States Department of Agricul- 

 ture have used colchicine to build an amazing series of straw- 

 berry plants. Fragaria vesca has 14 chromosomes, F. elaiior, 

 42, F. chiloensia and F. virginiana have 56. The cultivated 

 strawberry is directly derived from the last two and also has 

 56 chromosomes. In order to improve the cultivated straw- 

 berry in flavor, in disease resistance and drought resistance, 

 in shipping quality, etc., certain characters from all the above 

 species were desirable. Fertile crosses can be made only with 

 plants having the same chromosome numbers, therefore, 

 they set out to double the chromosome number of those with 

 larger as well as those with smaller numbers. By use of 

 colchicine and hybridizing they have actually made to order 

 a whole series of plants to be used in improving the straw- 

 berry. 



In all plant breeding or genetical work the various 

 methods of attack must be considered in order to select the 

 one best adapted to the problem and to the facilities of the 

 worker. It is well to keep in mind that by careful considera- 

 tion more than one good method of investigation will be 

 available to solve most problems. It is best to use as many 

 methods as are practicable. 



Careful observation of plants is of first importance. After 

 a mental picture of the desired plant has been formed, the 

 plants with these desirable characteristics must be sought. 

 Many worthwhile improvements have resulted from the 

 selection of plants produced by nature, as foundation stock. 

 Not all plants breed true, but here we must find plants with 

 the qualities we want and strive to develop them. 



Plant breeding is the method most commonly considered 

 to be important, but it might be well to bear in mind that 

 actually this method is best when it is the total of all 

 methods. By this method we usually think of cross-polli- 

 nating of flowers, which is the fundamental part of the sys- 



