544 Journal of Agricultural Research voi. xix. No. « 



Waid/ and Zavitz ^ being the most important of that reported in 

 America. It is safe to say, however, that the work done so far has not 

 by any means cleared up the subject of selection within clonal varieties. 

 At present we can not say that we have a clear vision of the possibilities 

 or the limitations along this line of plant breeding. Since plants within 

 clonal varieties vary, we have assumed that there is opportunity for 

 improvement through selection just as in varieties that are propagated 

 from seed. But to what extent we can make use of selection to perpet- 

 uate desirable variations within the clon and in this way improve these 

 varieties is still a question. 



The plant breeder recognizes in plants three types of variations: 

 (i) fluctuations or modifications, (2) segregations or combinations, and 

 (3) mutations. Fluctuations are such variations as appear as a result 

 of variable environmental conditions and are by many considered non- 

 heritable or nontransmittable from one generation to another, re- 

 gardless of whether perpetuation is through seeds or vegetative parts. 

 In other words, if we accept this theory of the nonheritability of fluc- 

 tuations due to environment we can not expect to increase the average 

 vigor of a potato variety by selecting seed tubers from especially vig- 

 orous hills so long as the variation in vigor might be attributed to 

 environmental conditions. Segregations are heritable differences 

 resulting from segregation and recombination of hereditary units. This 

 type of variation appears within the population of new hybrids and 

 crosses perpetuated by seeds rather than by vegetative multiplication. 

 Among potatoes we could expect such variations to appear only among 

 seedlings, and for this reason segregation can not be considered among 

 the possibilities for improving potato varieties which are perpetuated 

 vegetatively. Mutations are heritable variations which do not depend 

 upon segregation and recombination. Mutations are supposed to be 

 much rarer than the other variations mentioned. Among horticultural 

 plants many clonal varieties have arisen in this way and have for many 

 years been perpetuated true to type through vegetative multiplication. 

 An excellent example of a mutant among potatoes is the Pearl, which 

 originated as a mutation, or in common language, as a bud sport from 

 the Blue Victor. This has occurred not only once but several times. 

 In our own Blue Victor seed plot of 1918 there appeared such a varia- 

 tion. This mutant was a perfect Blue Victor with the exception that it 

 was white instead of blue in color. In other words, it was a perfect 

 Pearl. In this seed plot, seed pieces from each tuber were planted in 

 consecutive hills. The hills were thinned to single stems, and just one 



' Green. W. J., and Waid, C. W. potato investigations, spraying and seed selection experi- 

 ments; VARIETY TESTS. Ohio AgT. Exp. Sta. Bui. 174, p. 251-289, 18 fig. 1906. 



Waid, C. W. results of hill selection of seed potatoes. In Amer. Breeders' Assoc. Rpt., v. 3, 

 p. 191-199. 1907. 



'Zavitz, C. A. [report of the department of field husbandry.] In 31st Ann. Rpt. Ontario Agr- 

 Exp. Col. and Exp. Farm, 1905, p. 165-220. 1905. 



