4G 



THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



The beauty of Alpine flowers is almost prover- 

 bial. It consists either in the increased size of 

 the individual flowers as compared with the whole 

 plant, in increased intensity of color, or in the 

 massing of small flowers into dense cushions of 

 bright color ; and it is only in the higher Alps, 

 above the limit of forests and upward toward the 

 perpetual snow-line that these characteristics are 

 fully exhibited. This effort at conspicuousness 

 under adverse circumstances may be traced to 

 the comparative scarcity of winged insects in the 

 higher regions, and to the necessity for attracting 

 them from a distance. Amid the vast slopes of 

 debris and the huge masses of rock so prevalent 

 in higher mountain-regions, patches of intense 

 color can alone make themselves visible and serve 

 to attract the wandering butterfly from the val- 

 leys. Mr. Ilerman Muller's careful observations 

 have shown that in the higher Alps bees and 

 most other groups of winged insects are almost 

 wanting, while butterflies are tolerably abundant ; 

 and he has discovered that in a number of cases 

 where a lowland flower is adapted to be fertilized 

 by bees, its Alpine ally has had its structure so 

 modified as to be adapted for fertilization only 

 by butterflies. 1 But bees are always (in the tem- 

 perate zone) far more abundant than butterflies, 

 and this will be another reason why flowers spe- 

 cially adapted to be fertilized by the latter should 

 be rendered unusually conspicuous. We find, 

 accordingly, the yellow primrose of the plains re- 

 placed by pink and magenta-colored Alpine spe- 

 cies ; the straggling wild-pinks of the lowlands 

 by the masses of large flowers in such mountain 

 species as Dianthus alpinus and J), glacialis ; the 

 saxifrages of the high Alps with bunches of flow- 

 ers a foot long, as in Saxifraga longifolia and S. 

 cotyledon, or forming spreading masses of flow- 

 ers, as in S. opposififolia ; while the soapworts, 

 silenes, and louseworts, are equally superior to the 

 allied species of the plains. 



Again, Dr. Miiller has discovered that when 

 there are showy and inconspicuous species in the 

 same genus of plants, there is often a correspond- 

 ing difference of structure, those with large and 

 showy flowers being quite incapable of self-fer- 

 tilization, and thus depending for their very exist- 

 ence on the visits of insects ; while the others are 

 able to fertilize themselves should insects fail to 

 visit them. We have examples of this difference 

 in Malva sylveslris, Epilobium angnsiifolium, Poly- 

 gonum bistorta, and Geranium pratense — which 

 have all large or showy flowers and must be fer- 

 tilized by insects — as compared with Malva ro- 

 1 Nature, vol. xi., pp. 32, 110. 



tundifolia, Epilobium parviforum, Polygonum avi- 

 culare, and Geranium pusillum, which have small 

 or inconspicuous flowers, and are so constructed 

 that if insects should not visit them they are able 

 to fertilize themselves. 1 



As supplementing these curious facts showing 

 the relation of color in flowers to the need of the 

 visits of insects to fertilize them, we have the 

 remarkable, and on any other theory utterly in- 

 explicable circumstance, that in all the numerous 

 cases in which plants are fertilized by the agency 

 of the wind they never have specially colored 

 floral envelopes. Such are our pines, oaks, pop- 

 lars, willows, beeches, and hazel ; our nettles, 

 grasses, sedges, and many others. In some of 

 these the male flowers are, it is true, conspicuous, 

 as in the catkins of the willows and the hazel, 

 but this arises incidentally from the masses of 

 pollen necessary to secure fertilization, as shown 

 by the entire absence of a corolla or of those 

 colored bracts which so often add to the beauty 

 and conspicuousness of true flowers. 



The adaptation of flowers to be fertilized by 

 insects — often to such an extent that the very 

 existence of the species depends upon it — has had 

 wide-spread influence on the distribution of plants 

 and the general aspects of vegetation. The seeds 

 of a particular species may be carried to another 

 country, may find there a suitable soil and climate, 

 may grow and produce flowers, but if the insect 

 which alone can fertilize it should not inhabit 

 that country, the plant cannot maintain itself, 

 however frequently it may be introduced or how- 

 ever vigorously it may grow. Thus may probably 

 be explained the poverty in flowering plants and 

 the great preponderance of ferns that distin- 

 guishes many oceanic islands, as well as the de- 

 ficiency of gayly-colored flowers in others. This 

 branch of the subject is discussed at some length 

 in my address to the Biological Section of the 

 British Association, 2 but I may here just allude 

 to two of the most striking cases. New Zealand 

 is, in proportion to its total number of flowering 

 plants, exceedingly poor in handsome flowers, 

 and it is correspondingly poor in insects, espe- 

 cially in bees and butterflies, the two groups 

 which so greatly aid in fertilization. In both 

 these aspects it contrasts strongly with Southern 

 Australia and Tasmania in the same latitudes, 

 where there are a profusion of gayly-colored flow- 

 ers and an exceedingly rich insect-fauna. The 

 other case is presented by the Galapagos Islands, 

 which, though situated on the equator off the 



1 Nature, vol. ix., p. 164. 



8 See Nature, September 6, 1870. 



