JOURNAL 



OF THE 



Royal Hortioultdeal Society. 



Vol. XXXV. 1910. 

 Part III. 



THE PRODUCTION OF HORTICULTURAL VARIETIES. 

 By Professor Hugo de Vries. 

 [Being the second " Masters Lecture," read September 28, 1909.] 



The production of horticultural varieties has attracted the attention of 

 scientific men ever since Darwin pointed out its high significance for the 

 theory of evolution. According to him, varieties are only small species, 

 and if varieties can be produced by natural means, why not species also ? 

 A large part of Darwin's work was devoted to the critical examination 

 of the question, whether in this respect there is a real difference between 

 species and varieties or not. If once the common origin of species were 

 admitted, the same conclusion would hold for the natural families, and 

 even for the larger groups of the vegetable and animal kingdom. The 

 main question was the origin of the species, and the main argument was 

 the direct observation of the origin of varieties in horticultural and in 

 agricultural practice. 



The production of varieties having thus come to possess a far-reaching 

 scientific significance, it became of interest to submit it to a sharp 

 criticism. There can be no doubt that it really proves the main pro- 

 position. But we should like to know the process in its details, and the 

 question arises, how far these are available for scientific purposes. It 

 does not necessarily follow from the evolution theory that species in 

 nature are produced in actually the same manner as varieties are in 

 horticulture. The general laws governing the process must, of course, 

 be the same in both cases, but the details may be different. 



In horticultural practice the effects of accidental crossing especially 

 play a large part in the nurseries, where, as a rule, numerous allied 

 species and varieties are cultivated close to one another. The process 



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