68 Mutability and Individual Variation. 



He includes mutations or spontaneous variations under 

 the term heterogenesis on the analogy of Kolliker^s 

 heterogenetic reproduction and the "Heterogenism" of 

 Hartmann.^ He bases his conclusions on the data of 

 horticultural practice and gives a complete and very im- 

 portant survey of the cases in which the history of the 

 first appearance of varieties is more or less accurately 

 known, or in which the occurrence of new forms other 

 than by a series of transitional stages points to a sudden 

 origin. 



Such heterogenetic changes (the mutations of the 

 older investigators) can be progressive or retrogressive, 

 that is the organs can become more complicated or more 

 simple ; both kinds of changes must often happen, but 

 the retrogressive ones can obviously occur more easily 

 than progressive ones. Mutations can be induced, as 

 Darwin also believes, by the cumulative operation of 

 favorable conditions during development and by rich 

 nutrition continued through many generations. Forms 

 that have newly arisen can sometimes be so sharply dis- 

 tinguished from the parent type that any systematist 

 would take them for a separate species if he did not know 

 their origin. 



Korschinsky concludes from a survey of the facts 

 at his disposal that among garden plants all new forms, 

 or more strictly all new characters, have originated by 

 heterogenesis. New varieties are not obtained in horti- 

 culture by the selection or cumulation of individual differ- 

 ences. Selection is a conservative agency. It fixes new 



^ S. Korschinsky, Heterogenesis und Evolution, Naturzvissen- 

 schaftlichc Wochenschrift, 1899, Vol. XIV, No. 24. A larger work 

 appeared in the Mcmoircs of the St. Petersburg Academy of Sciences, 

 1899, Vol. IX. See also Flora, Vol. 59, 1901, pp. 240-363. (Note 

 of 1908). 



