Chap. XV. OF THE MODIFICATION OF EACES. 99 



itself; but it is now positively affirmed 34 that this is an error. 

 With plants which can be multiplied by buds and cuttings, hybri- 

 disation has done wonders, as with many kinds of Roses, Rhodo- 

 dendrons, Pelargoniums, Calceolarias, and Petunias. Nearly 

 all these plants can be propagated by seed; most of them 

 freely ; but extremely few or none come true by seed. 



Some authors believe that crossing is the chief cause of varia- 

 bility, — that is, of the appearance of absolutely new characters. 

 Some have gone so far as to look at it as the sole cause ; but 

 this conclusion is disproved by some of the facts given in the 

 chapter on Bud-variation. The belief that characters not present 

 in either parent or in their ancestors frequently originate from 

 crossing is doubtful ; that they occasionally thus arise is pro- 

 bable ; but this subject will be more conveniently discussed in 

 a future chapter on the causes of Variability. 



A condensed summary of this and of the three following 

 chapters, together with some remarks on Hybridism, will be 

 given in the nineteenth chapter. 



3i Dr. Pigeaux, in • Bull. Soc. d'Acclimat.,' torn, iii., July 1866, as quoted in 

 'Annals and Mag. of Nat. Hist.,' 1867, vol. xx. p. 75. 



TI "Z 



