588 THE GENESIS OF NEW SPECIES. 



a numerous progeny. Sometimes such suitability does exist, but sometimes also it 

 does not. In the latter case the hybrid is suppressed as soon as it sees the light. 

 But even if its organization is adapted to the soil and climate of the place of origin, 

 it has to enter upon a struggle with the species already established there, and 

 especially with its own parent-species. If the latter grow luxuriantly and in large 

 numbers at the spot, it is not easy for the new form to take possession of the 

 ground. In two cases only is there any prospect of the place of origin becoming a 

 permanent home for the hybrid's descendants: firstly, where the hybrid, in virtue 

 of its particular attributes, is equally well, or perhaps even better adapted to the 

 habitat of the parent-species than are the plants already established there, and 

 secondly, when the hybrid originates at a spot more or less removed from the place 

 where the parent-species grow and encounters conditions of soil and climate which 

 agree with it better than with the parent-species. 



That these conditions of the origin of species from hybrids are sometimes 

 fulfilled will now be shown by a few examples. In the Tyrolese Alps, to the 

 south of Innsbruck, at the head of the valleys known as the Stubaithal and the 

 Gschnitzthal, there are certain mountains which rise steeply to a height of from 

 2500 to 3000 metres. The base of these mountains is composed of crystalline 

 schist; midway up their ascent mixed strata of schist and limestone are encoun- 

 tered ; and above these strata there is limestone and also dolomite, rising abruptly 

 and forming the peaks and ridges. Half-way up the sides, where the soil exhibits 

 great variety, an extraordinarily rich flora is developed. Plants which are, except 

 in this instance, peculiar to schist formations, and others usually only found on 

 limestone, here grow close together. Amongst other species the Alpine Roses, 

 Rhododendron ferrugineum and R. hirsutum, grow side by side on the same soil 

 and on the same slopes. Associated with them is a third species of Alpine Rose, 

 Rhododendron intermedium, which has sprung from the crossing of R. ferru- 

 gineum and R. hirsutum. At several places, e.g. on the eastern and northern 

 slopes of the Hohe Burgstall, in the Stubaithal, and on the Padaster Alp in the 

 Gschnitzthal, Rhododendron interm^edium occurs more commonly than either of 

 the parent-species. Like the latter, it grows on soil rich in humus, flowers 

 abundantly, develops fruits with fertile seeds, and transmits its characteristics 

 unaltered to its descendants. Here and there isolated plants are found which must 

 be ranked as goneoclinic hybrids, but plants of Rhododendron intermedium form 

 the larger proportion of the Alpine Roses which clothe the mountain-sides. This 

 form accords in every particular with the requirements demanded of a species, and 

 is quite as much a systematic entity as either R. ferrugineum or R. hirsutum. 

 The following is the explanation of how this has come to pass: The colour of the 

 flowers is a little lighter than in R. ferrugineum and richer than in R. hirsutum; 

 it is a brilliant carmine tint, and enables one even at a distance to identify every 

 plant of the hybrid. Hive- and bumble-bees hovering about in search of honey 

 are more attracted by flowers of R. intermedium than by the others, owing to 

 the superior brilliancy of their coloration, and the result is that these flowers are 



