v.] VAN MONS AND KNIGHT. 157 



vinced that all varieties of fruit trees ' ' become subject 

 within no very distant period to the debilities and dis- 

 eases of old age," and that each variety has a "most 

 productive and eligible" epoch, and that this epoch 

 occurs whilst the variety is still young; or, as Knight 

 expresses it, "the most prolific period is that which im- 

 mediately succeeds the age of puberty." That is, vari- 

 eties are strongest and most productive early in their 

 existence, and thence tend to gradually fail. He also 

 maintained that the eions of any seedling tree cannot be 

 "made to produce blossoms or fruit till the original tree 

 has attained its age of puberty, ' ' and that the longevity 

 and behavior of any variety are intimately connected 

 with the behavior of the original seedling from which 

 the variety had its birth. These ideas were suggested 

 by experiment and observation, for he tells us that he 

 was first convinced "that each varietj^ possessed its 

 greatest value in its middle age," but certain experiments 

 led him to change his views. This dogmatic hypothesis 

 of the duration of varieties was widely repeated, but it 

 appears, fortunately, never to have exerted great influ- 

 ence, and it is so insignificent in comparison with 

 Knight's greater M^ork that we need not dwell further 

 upon it. 



Van Mons was the first horticulturist to boldly ex- 

 emplify and demonstrate the value of the great prin- 

 ciple of repeated selection in the origination of varieties. 

 Knight was the first to show the value of crossing for 

 the same purpose. Kcelreuter, at the middle of the last 

 century, had made many suggestive experiments in the 

 crossing of plants, but his studies were concerned 

 with the immediate means and effects of the operation. 

 Sprengel, at the close of the century, had observed 



