22 Descent 



tral line. This, and approximately this only, is 

 the essential difference between experimental 

 and accidental observation. 



Mutations are occurring from time to time in 

 the wild state as well as in horticulture and 

 agriculture. A selection of the most interest- 

 ing instances will be given later. But in all 

 such cases the experimental proof is wanting. 

 The observations as a rule, only began when the 

 mutation had made its appearance. A more or 

 less vague remembrance about the previous 

 state of the plants in question might be avail- 

 able, though even this is generally absent. But 

 on doubtful points, concerning possible crosses 

 or possible introduction of foreign strains, mere 

 recollection is insufficient. The fact of the mu- 

 tation may be very probable, but the full proof 

 is, of course, wanting. Such is the case with 

 the mutative origin of Xanthium commune 

 Wootoni from New Mexico and of Oenothera 

 biennis cruciata from Holland. The same 

 doubt exists as to the origin of the Capsella 

 Heegeri of Solms-Laubach, and of the oldest 

 recorded mutation, that of Chelidonium lacinia- 

 tum in Heidelberg about 1600. 



First the unavoidable doubt about the fact it- 

 self. This however, gradually loses its impor- 

 tance in the increasing accumulation of evi- 

 dence. Secondly, the impossibility of a closer 



