Tlie Evidence from Variation. 145 



produced from bads only in their greater tendency to 

 vary. Bud variations do occur, but they are very un- 

 usual, while more or less variation in seedling plants is 

 almost universal. 



As we suppose that any cell may, when excited by 

 unfavorable conditions, throw off gem mules, the gem- 

 mules may find their way, by a sort of accident, to 

 growing buds, and thus cause variation. We should 

 therefore expect bud variation to occur occasionally, 

 but very much less frequently than variation in seed- 

 lings. 



This is so well known to be the case that many authors 

 have held that there can be no variation without sexual 

 union. Darwin has shown, however, by a long list of 

 instances of bud variation in plants, that this is not 

 absolutely true, and the weight of his authority has led 

 to the almost universal acceptance of his conclusion that 

 there is no essential difference between asexual and sexual 

 heredity. I shall discuss this conclusion at length in 

 another place, as I believe that the facts demand an in- 

 terpretation which is somewhat different from the one 

 which Darwin furnishes. At present I simply wish to 

 call attention to the fact that all authorities agree that 

 variation is almost infinitely more common in sexual than 

 it is in asexual offspring. 



Asexual multiplication in animals is restricted to the 

 lower forms which are of little use to man, and as these 

 forms have not been domesticated and carefully observed, 

 our knowledge of the variability of organisms produced 

 asexually is almost entirely derived from the study of 

 plants. 



The only instance in domesticated animals of anything 

 like asexual reproduction is the parthenogenetic repro- 

 duction of bees, and it is therefore interesting to note 



