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Show 316 DARWINISM CHAP. debted to the ex:.tct and long-continued researches of Professor Hermann Muller. Su,rnrna1·y of Additional Facts bearin,q on Insect Fertilisation. 1. That the size and colour of a flower are important factors in determining the visits of i~1sects, is shown by the general fact of more insects visiting conspicuous than in~onspicuous flowers. As a single instance, the handsome <?-~ranmm palustre was observed by I rofessor Muller to be VISited hy sixteen different , pecies of insects, the equally showy G. pratense by thirteen species, while the smaller and much less conspicuous G. molle was visited by eight species, and G. pusillum by only one. In many cases,. howe~er, a flower may be very attractive to only a few species of msects ; an<l Pr~fessor Miiller states, as the result of many years' assiduous observation, that "a species of flower is the more visited hy insects the more conspicuous it is." 2. Sweet odour is usually supplementary to the attraction of colour. Thus it is rarely present in the largest and most gaudily coloured flowers which inhabit open places, such as poppies, proonies, sunflowers, and many others; while it is often tlH' accompaniment of inconspicuous flowers, as the mignonette; of such as grow in shady places, as the violet and primro. e; nncl esp cially of white or yellowish flowers, as tho white jasmiw'. clematis, stephanotis, etc. 3. v\Thite flowers are often fertilised by moths, and very frequently give out their scent only by night, as in our butterflyorchis (Habenaria chlorantha); and they sometimes open only <1t night, as do many of the evening primroses and other fl owers. These flowers are often long tubed in accordance with tho length of the moths' probosces, as in the genus Pancratim' ., our butterfly orchis, white j:.tsmine, and a host of other .. 4. Bright reel flowers are very attractive to butterflies, an<l arc sometimes specially adapted to be fertilised by them, as in many pinks (Dianthus deltoides, D. superbus, D. atroruhcns), the corn-cockle (Lychnis Githago), and many others. Hlno flowers are especially attractive to bees and other hymcnoptcra (though they frequent flowers of all colours), no less than sixtyseven species of this order having been observed to visit the common "shecp's-hit" (Jasione montana). Dull yellow or XI THE SPECIAL COLOURS OF PLANTS 317 brownish flowers, some of which smell like carrion a,re attractive _to flies, as the Arum and Aristolochia; whil~ the ~ull purphsh flowers of the Scrophularia are specially attractive to wasps. 5. S?me flowers have neither scent nor nectar, and yet attrac~ I~sects by sham_ nectaries! In the herb-paris (Paris quadrifoha) the ovary ghstens as if moist, and flies alight on it and carry away pollen to another flower; while in grass of parnassus (Parnassia palustris) there are a number of small stalked yellow balls near the ba. c of the flower which look like drops of honey but arc really dry. In this' ca. c there is a little nectar lower clown, bnt the pecial attraction i. a sham; _and as there arc fresh broods of insects every year, it takes titne for t~em to learn by experience, and thu. · enough are always decmved to effect cross-fertilisation.I Thi is analogous to the case of the young birds, which have to learn by experience the insects that arc inedible, as explained at page 253. 6. Many flowers change their colour as soon as fertilised · and this is beneficial, as it enables bees to avoid wastina tim~ in visiting those blossoms which have been already fm~ili ed and their nectar exhausted. The common luncrwort (Pulmonaria officinalis ), is at first red, but later turn~ blue · and H. Muller observed bees visiting many reel flowc;·. in succession, but neglecting the blue. In South Brazil there is a species of Lantana, whose flowers are yellow the first day, orange the second, and purple the third ; and Dr. Fritz Muller observed that many butterflies visited the yellow flowers only, some both the yellow and the orange flowers, but none the purple. 7. Many flowers have markings which serve a crnides to . . 0 msects; m some cases a bright central eye, as in the borage and forget-me-not; or lines or spots convere:ina to the centre • • u b ' as m geramums, pinks, and many others. This enables insects to go quickly and directly to the openino· of the flower, and is equally important in aiding them to ~btain a better supply of food, and to fertilise a larger number of flowers. 8. Flowers have been specially adapted to the kinds of 1 Mi.iller's Fert-ilisation of Flowers, p. 248. |