August 3, 1882] 



NA TURE 



523 



THE COLOURS OF FLOWERS, AS ILLUS- 

 TRATED BY THE BRITISH FLORA 1 

 II. — Further Examples of the General Law 

 "C* LOWERS in which the carpels have arranged them- 

 -*• selves in a circle around a common axis, like the 

 Geraniacecc and Malvacav, thereby show themselves to 

 be more highly modified than flowers in which all the 

 carpels are quite separate and scattered, like the simpler 

 Rosacea and Ranunculacea. Still more do families such 

 as the Caryophyllacece, in which all the five primitive 

 carpels have completely coalesced into a single one-celled 

 ovary. Accordingly, it is not remarkable that the pinks 

 should never be yeliow. On the other hand, this family 

 has no very specialised members, like larkspur and 

 monkshood, and therefore, it very rarely produces bluish 

 or purplish flowers. Pinks, in fact, do not display so 

 wide a range in either direction as Ranunculaccce. They 

 begin as high up as white, and hardly get any higher than 

 red or carnation. Of their two sub-families, the Alsincce 

 have the sepals free, the blossoms widely expanded, and 

 no special adaptations for insect fertilisation. They in- 

 clude all the small undeveloped field species, such as the 

 chickweeds (Stellaria media, Arenaria trinervis, Ceras- 

 tium viilgaliim, &o.), stitchworts (Stellaria holostea, &c), 

 and cornspurries (Spergula arvensis), which have open 

 flowers of a very primitive character ; and almost all of them 

 are white (Fig. 12). These are fertilised by miscellaneous 

 small flies. The Silenear, on the other hand, including 

 the campions and true pinks, have a tubular calyx, formed 

 by the coalescence of the five sepals ; and the expanded 

 petals are raised on long claws, which makes their honey, 

 inclosed in the tube, accessible only to the higher insects. 

 Most of them also display special adaptations for a better 

 class of insect fertilisation in the way of fringes or crowns 

 on the petals. These more profoundly modified kinds 

 are generally pink or red. For example, in the most 

 advanced British genus, Dianlhits, which has usually 

 vandyked edges to the petals, our four English species 

 are all brightly coloured ; D. armeria, the Deptford pink, 

 being red with dark spots, D. prolifer purplish red, D. 

 deltoidcs, the maiden pink, rosy spotted with white, and 

 D. casiiis, the Cheddar pink, bright rose-coloured (Fig. 

 '3). 



It is much the same with the allied genus Lychnis. Our 

 own beautiful purple English corn-cockle (L. githagd), is 

 a highly developed campion, so specialised that only 

 butterflies can reach its honey with their long tongues, as 

 the nectaries are situated at the bottom of the tube. Two 

 other species of campion, however, show us interestingly 

 the way in which variations of colour may occur in a 

 retrograde direction even among highly evolved forms. 

 One of them, the day lychnis (L. diuruaj, has red, scent- 

 less flowers, opening in the morning, and it is chiefly 

 fertilised by diurnal butterflies. But its descendant, the 

 night lychnis (L-vespertina), has taken to fertilisation by 

 means of moths ; and as moths can only see white flowers 

 it has become white, and has acquired a faint perfume as 

 an extra attraction (Fig. 14). Still, the change has not 

 yet become fully organised in the species, for one may 

 often find a night lychnis at the present time which is 

 only pale pink, instead of being pure white. 



The Crucifera are a family which display a good deal 

 of variety in colouration. The most primitive and simple 

 forms have yellow flowers, as in the case of the cabbage 

 genus (Brassica) including charlock, mustard, and turnip ; 

 the rockets (Barbarca and Sisymbrium) ; and the gold- 

 of-pleasure (Camelina saliva). Most of these are dry-field 

 weeds, and they have open little-developed blossoms. In 

 the genus Nasturtium or watercress we have four species, 

 three of which are yellow, while one is white. In treacle- 

 mustard (Erysimum), the yellow is very pale, and the 

 petals often become almost white. Just above these 



1 Continued from p. 304. 



earliest forms come the common small white crucifers 

 like Cardamine hirsuta, Cochlearia officinalis, and Cap- 

 sella bursa-pastoris. Many of these are little if at all 

 superior in organisation to the yellow species, and some 

 of them (as we shall see hereafter) are evidently degenerate 

 weeds of cultivation. But such flowers as Alyssum mari- 

 timum, with its sweet scent, its abundant honey, its re- 

 duced number of seeds, and its conspicuous, spreading 

 milk-white petals, are certainly more developed than 

 small yellow species like Alyssum calycinum. Even 

 more remarkably is this the case in the genus Herts or 

 candytuft, which has become slightly irregular, by the 

 two adjoining exterior petals growing larger than the 

 interior ones. Accordingly, they are usually white, like 

 our British species, /. ainara; while some of the larger 

 exotic species are a pretty pink in hue. The genus Car- 

 damine supplies us with like instances. Here the smaller 

 species have white flowers, and so has the large C. ainara. 

 But in C. pratensis, the cuckoo-flower, they are usually 

 tinged with a pinkish purple, which often fades deep 

 mauve ; and in some showy exotic species the flowers are 

 a rich pink. So with Arabis : our small English kinds 

 are white ; A . petrcea, with larger petals, is often slightly 

 purplish, and some handsome exotics are a vivid purple. 

 In Hesperis we get a further degree of modification in 

 that the petals are raised on rather long claws ; and the 

 flowers (represented in England by H. matroualis, the 

 dame's-violet) are a fine purple, and possess a powerful 

 perfume. Closely allied is the Virginia stock of our 

 gardens (Malcolmia), which varies from pale pink to 

 mauve. But the highest of all our crucifers are contained 

 in the genera Mattkiola and Chciranthus, which have 

 large spreading petals on long erect claws, besides often 

 being sweet scented. The common stock (.1/. incand) is 

 purple, reddish, or even violet; our other British species, 

 M. sinuata, is pale lilac ; and no member of the genus is 

 ever yellow. The wall-flower (Chciranthus cheirt) is rich 

 orange or red, sometimes yellow : its colour, however, 

 differs widely from the primitive yellow of the charlocks 

 or buttercups ; and it will receive further attention here- 

 after. 



So much by way of illustration of the families with 

 usually regular polypetalous flowers and free superior 

 ovaries. We may next pass on to the families of poly- 

 petalous flowers with usually irregular corollas, which 

 represent of course a higher stage of development in 

 adaptation to insect visits. Of these, two good illustrative 

 cases are included in the British flora. They are the 

 Polygalacea and the Violacece. 



Polygala vulgaris, or milkwort, our only British repre- 

 sentative of the first named family, is an extremely irre- 

 gular flower, very minutely and remarkably modified for 

 special insect fertilisation. It is usually a bright blue in 

 colour, but it often reverts to pink, and not infrequently 

 even to white. 



The Violacece or violets are a whole family of bilateral 

 flowers, highly adapted to fertilisation by insects ; and as 

 a rule they are a deep blue in colour. This is the case 

 with four of our British species, Viola odorata, V. canina, 

 V. hi/la, and V. palustris. Here too, however, white 

 varieties easily arise by reversion ; while one member of 

 the group, the common pansy, V. tricolor, is perhaps the 

 most variable flower in all nature. This case, again, will 

 receive further attention when we come to consider the 

 subject of variegation and of reversion or retrogression. 



When we pass on to the Corollifloree, in which the 

 originally separate petals have coalesced into a single 

 united tube, we meet with much more striking results. 

 Here, where the very shape at once betokens high modi- 

 fication, yellow is a comparatively rare colour (especially 

 as a ground-tone, though it often comes out in spots or 

 patches), while purple and blue, so rare elsewhere, become 

 almost the rule. 



The family of Campari ulacece forms an excellent ex- 



