Conclusion. 503 



took place (this species being exclusively female), the 

 pollen of O. Lamarckiana being generally used for the 

 purpose. 



Thus each family has a single and pure main stock. 

 Branches of it are to be regarded as separate families. 

 The mutations arose from these main stocks. 



The great advantage of this method is tliat it enables 

 us to knov^ the ancestors of each mutation through one 

 or more generations. And this is just what is lacking 

 in observations made in the field, and in horticultural 

 data. The number of generations known is great in 

 direct proportion as the date of the mutation in question 

 is recent. The pedigree of every single mutation can be 

 determined in my records, and found to be, for exami)le, 

 a pure line of Lamarckiana, or laevifolia or riihrincrvis 

 or lata, and so forth, according to the family.^ One 

 would like to complete the series of ancestors for the 

 period of time previous to the year 1886, in which I 

 first collected seeds and plants. I have no direct obser- 

 vations wdiich will help us ; but it is known that the plant 

 began to spread over the field about 1870. It is highly 

 probable that new forms, if they had flowered during 

 these years, would have been found flowering afterwards 

 in the field also, after the rapid multiplication which had 

 taken place. We may therefore consider ourselves justi- 

 fied in mentally carrying back the pure unbroken line to 

 1870. 



The individual mutations in the various families arise 



wholly independently of one another ; that is to say each 



one arises directly from the main stem. If we harvest 



the seed of mutants, or fertilize other plants with their 



*The pedigrees for the 3 chief families can be found on the fol- 

 lowing pages: Lamarckiana-i^mWy, pp. 224 and 262; lacvitoha-iiww- 

 ily, p. 2"/ 2,', /a/a-family, pp. 285 and 288. 



