200 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
of opinion exists. I need not enumerate them further, and I believe 
that a deeper search among the scattered records'would add several to 
the foregoing list of those whose origin has been demonstrated experi- 
mentally. 
There is one question remaining on which I should like to say a few 
words, and that is whether the question of hybridisation may not have 
to be considered even in connection with the very origin of species. 
Kerner answers the question whether “ species”? are ever produced by 
hybridisation in the affirmative, and adduces some very important evidence 
in support of this view. In discussing it we need not go into the vexed 
question of what is a species. We may take it that they exist, and for 
the sake of clearness may adopt the Darwinian conception that they have 
arisen by gradual divergence of character from a common ancestor. We 
have already seen that certain hybrids are fertile, and can be reproduced 
true from seed for years in succession. We may therefore term them 
“hybrid races,” but we may ask, in what respect, apart from their origin, 
which is known, can they be distinguished from certain “ species,’’ univer- 
sally recognised as such, whose origin is not known? If difference there 
be, we are not yet able to define it in words. 
Kerner, in his ‘‘ Natural History of Plants,’’ has given some interesting 
particulars about these hybrid races, from which we may make a few 
extracts. A hybrid between Medicago falcata and sativa, known as 
M. media, is widely cultivated as a fodder plant, and is propagated from 
seed (vol. ii. p. 577). Salvia betonicefolia, a hybrid from S. nemorosa 
and nutans, is aS common as its parents in grassland in Central Hun- 
gary (p. 585). Betula alpestris, a hybrid between B. alba and nana, is 
abundant in the Jura, Scandinavia, and in North Russia, here and there 
whole copses of it being found (p. 586). Nigritella swaveolens, a hybrid 
between N. angustifolia and Gymnadenia conopsea, is abundant in some 
Swiss localities, hundreds of plants sometimes occurring in a single 
meadow (p. 586). Hybrids between the Primrose and Cowslip occur in 
thousands in upland meadows in the Eastern Alps (p. 586). 
Rhododendron intermedium is a particularly interesting hybrid. In 
some localities in the Tyrol there is a great variety of soil, and a very 
rich flora, plants peculiar to schist formations and others found only on 
limestone growing close together. Rhododendron ferruginewm and 
R. hirsutum, though peculiar to these formations respectively, thus exist 
here side by side, and intercross freely, the hybrid in some localities being 
commoner than either parent. It seeds freely, and comes true from seed, 
and thus fulfils all the requirements demanded of a species, being as 
much a specific entity as either parent. The explanation is that the 
flowers are a little lighter than those of R. ferrugimewm, but richer than 
R. hirsutum; in fact, a brilliant carmine, which enables every plant to 
be identified at a distance. It is thus more attractive to bees, and gets 
fertilised with its own pollen. In some localities, where detritus from 
the limestone occurs mixed with humus, the hybrids do better than R. 
ferrugineum, and as wellas R. hirsutwm, so that it has an advantage 
over the former in the matter of soil, and over both parents so far as 
insect visits are concerned. It has thus a better chance of surviving 
(p. 588). 
