ON HYBEIDIZATION AMONG PLANTS. 
313 
take. Cultivated plants are not usually in their natural conditions. 
Their very tendency to break out into new forms appears to be 
an attempt of adaptation of the species to new media and 
circumstances ; so that the stability of character would seem 
less to be depended upon than if natural conditions were pro- 
vided, and genuine wild forms selected for operations. 
Nevertheless, we cannot but think M. Naudiffis experiments 
to have very satisfactorily shown that reversions do take place, 
at least amongst cultivated plants ; though it would seem to 
occur rarely among individuals in a wild state (Gaertner). 
And Wichura^s observations on willows agree with this, for he 
found nothing of the sort with sueh hybrids. 
6. Are there any exceptions to the law of return of hybrids 
to the parent form ? And do certain hybrids become fixed, and 
give rise to new species ? 
He mentions Regel as of that opinion, although he himself 
thinks it more probable that true species only arise from other 
species by variation — u by subdividing with secondary species.” 
Herbert remarks that “ the hybridizing process is to a certain 
extent inimical to fertility in the offspring,” and Wichura has 
the following : — 
The constantly-increasing sterility of hybrids, and their dying out when 
fertilized with their own pollen ” .... is accounted for by the fact 
that “ if a hybrid is fertilized for successive generations with its own pollen, 
individuals come together which have the same weak point, viz., that of repro- 
duction. The increase of weakness and sterility, and the rapid dying out of 
hybrids by continual impregnation with their own pollen, agrees with Darwin’s 
views of interbreeding causing sterility in successive generations. 
In conclusion, we would remark that there is yet much to 
learn from the investigation of hybridism ; and that a careful 
perusal of the writings of the best observers here and abroad 
impress us with the great difficulty there must necessarily be 
in arriving at satisfactory results in many cases. In fact, they 
so depend upon the mysterious laws of life, and the causes of 
sterility are so complicated and interwoven, that we doubt 
whether they can be entirely solved. Nevertheless, experi- 
ments may yet clear up many points, and furnish us with 
considerable help towards unravelling the phenomena of 
hybridization. 
