HYBRIDS 



Mutation tn (JLnothera lamarckiana. 



(The horizontal lines show successive generations, invariably obtained 

 onljf by sowing seeds of the ordmary form.) 



Since it has been snggestcd that De Vries' mutants sprang 

 from an original!}- h}-brid stock (cf. below), it may be mentioned 

 that other instances of mutation have since been described in 

 which the pure-bred character of the original strain appears to 

 be beyond question. Moreover, mutations do not occur only in 

 plants raised from seed, where as a consequence two gametes 

 are involved. The propagation of vegetative mutations, or sports, 

 which first appear only on a few branches of the plant, has 

 given rise to the Copper Beech, and to the cut-leaved varieties 

 of Alder, Beech (Fig. 223), etc. 



Another mode of origin of new forms is due to the recom- 

 bination of characters which takes place when two different 

 races, varieties, or species are employed as the respective parents. 

 In such cases the fertilised eggs are, of course, produced by the 

 participation of both parents, one furnishing the female and the 

 other the male sexual cell. Such " crossing " is often a failure, 

 no seed being set, but when successful the next generation is 

 found to show a mixture of the characters of the two parents, 

 some belonging to the one and some to the other. 



In respect to any single contrasting feature {e.g. height, hairi- 

 ness, etc.), however, the character of one or other parent fre- 

 quently altogether predominates {i.e. the offspring all show the 

 one feature), although sometimes the hvbrid is intermediate 

 between the two (cf. p. j&y). Since the characteristics of both 

 parents must luux been inherited, those of the one must, in 

 the former case, be supposed to remain dormant, or, as is 

 usually said, latent. As a matter of fact, if such hybrid plants 



