INSECURE INTERPRETATIONS 137 



It would be bold indeed to give instances of seed-atavism, 

 and I believe that it will be better to refrain wholly from doing 

 so. . . , It is by far safer in the present state of our know- 

 ledge to accept bud-variations only as direct proofs of true 

 atavism. And even these may not always be relied on, as 

 some hybrids are liable to split up in a vegetative way, and in 

 doing so to give rise to bud- variations that are in many respects 

 apparently similar to cases of atavism " (1905, p. 176). 



§ 9. Interpretations in Terms of Reversion 



As in many other cases, one of the difficulties in regard to the 

 reversion theory is that in terms of it much can be interpreted 

 and relatively little demonstrated. In regard to the origins 

 of domesticated animals and cultivated plants, we remain in 

 great obscurity. In regard to the actual pedigree of wild species 

 our ignorance is even greater. Thus, while it is often easy to 

 interpret an unexpected variation as a reversion to a plausible 

 ancestral type, we have little security in so doing. 



Thus De Vries distinguishes between experimentally demon- 

 strable reversion and what he calls " systematic atavism/' where 

 the ancestral type is merely presumed to be so-and-so on the 

 basis of taxonomic considerations. 



It is probable that the common ancestors of the " elementary 

 species " {Primula officinalis, P. elatior, and P. acaulis), which 

 make up the systematic species of primrose. Primula vera, were 

 " perennial plants with a rootstock bearing their flowers in 

 umbels or whorls on scapes. Lacking in Primula vera, these scapes 

 must obviously have been lost at the time of the evolution of 

 this form." But in the common acaulescent " elementary 

 species," P. acaulis, a scape sometimes develops. It may be 

 reasonably interpreted as due to the re-vitalising of a dormant 

 scape-character inherited from the presumed ancestor. " Simi- 

 larly with the appearance of bracts in the usually bractless 



