August 10, 1882] 



NATURE 



349 



only the ray-florets ligulate, or than the Cynaroidca-, which 

 have no ligulate florets at all. Hence we should naturally 

 expect them to be blue or purple, whereas they are for the 

 most part yellow of a very primitive golden type, while 

 the ray-florets of the Corymbifers are usually white or 

 pink, and all the florets of the Cynaroids are usually 

 purple. The following hypothetical explanation is sug- 

 gested as a possible way out of this difficult}-. 



The primitive ancestral composite had reached the 

 stage of blue or purple flowers while it was still at a level 

 of development corresponding to that of the scabious or 

 Jasione. The universality of such colours among the 

 closely allied Dipsacecc, Valerianea, Lobeliaeea, and 

 Campanulacea, adds strength to this supposition. The 

 central and most primitive group of composites, the 

 Cynaroids, has kept up the original colouration to the 

 present day : it includes most of the largest forms, such 

 as the artichoke, and it depends most of any for fertilisa- 

 tion upon the higher insects. All our British species 

 (except the degenerate Carlimi) are purple, sometimes 

 reverting to pale pink or white, while Cenlaurea cyanus 

 (Fig. 25), our most advanced representative of the tribe, 

 rises even to bright blue. 



Next to the Cynaroids in order of development come 

 the Corymbifers, some of which have begun to develop 

 outer ligulate rays. Here the least evolved type, Eupa- 

 torium. with few and relatively large florets, is usually 

 purple or white, never yellow. But as the florets grew 

 smaller, and began to bid for the favour of many miscel- 

 laneous small insects, reversion to yellow became general. 

 In a few cases here and there we still find purple or white 

 central florets, as in Petasites vulgaris, the butter-bur ; 

 but even then we get closely related forms, like Tussilago 

 farfara, colts-foot, which have declined to yellow. The 

 smallest and most debased species, such as Solidago 

 virga-aurea, golden rod, Tanacetum vu/gare, tansy, and 

 Senecio vulgaris, groundsel, have all their florets yellow 

 and similar ; unless, indeed, like GnaphaUum and Filago, 

 cud-weed, Artemisia absinthium, wormwood, or Xan- 

 tliium strumariuin, burweed, they have declined as far as 

 colourless or green florets, in which case they must be 

 considered under our next head, that of Degeneration. 

 On the other hand, the larger and better types of Corym- 

 bifers began a fresh progressive development of their 

 own. In many Senecios, Iiiulas, Chrysanthemums, they 

 produced yellow ray florets, similar in colour to those of 

 the disk. In Chrysanthemum leucanthemum, Anthemis 

 cotula, Matricaria ittodora, &c, these rays, under the 

 influence of a different type of insect selection, became 

 white. In the daisy they begin show signs of pink, and 

 in the Asters, Cinerarias, &c, they become lilac, purple, 

 and blue. Complicated as these changes seem, they must 

 yet have taken place two or three times separately in 

 various groups of Corymbifers, for example, in the 

 Asteroidea, the Anthemidea, and the Senecionida. 



The Ligulates were again developed from yellow-rayed 

 Corymbifers by the conversion of all the disk florets into 

 rays. Appealing for the most part to very large and varied 

 classes of miscellaneous insects, they have usually kept 

 their yellow colour (Fig. 26); but in a few cases a fresh pro- 

 gressive development has been set up, producing the 

 violet-blue or purple florets of the salsify ( Tragopogon 

 porrifolius), the deep blue Sonchus alpinus, and the bright 

 mauve succory, Ciclwrium intybus. As a whole, however, 

 the Ligulates are characterised by what seems a primitive 

 golden yellow, only occasionally rising to orange-red or 

 primrose in a few hawkweeds. 



That this hypothetical explanation may be the true one 

 seems more probable when we examine the somewhat 

 similar case of the Slellata. Here it seems pretty clear 

 that mere dwarfing of the flowers, by throwing them back 

 upon earlier types of insect fertilisation, has a tendency 

 to produce retrogression in colour. Even in the more 

 closely allied Dipsacece, Valerianea, and Campanulacea:, 



we see a step taken in the same direction, for while the 

 large-flowered Campanulas and Scabiosas are bright blue, 

 the smaller flowered teasel (Dipsacus silvestris) is pale 

 lilac, the Valerianas are almost white, and the i'aleriau- 

 el/as are often all but colourless. In the Stellate, the 

 same tendency is carried even further. As a whole, these 

 small creeping weeds of the temperate regions form a 

 divergent group of the tropical Rubiacem (including Cin- 

 ckomacece), from which they are clearly derived as a 

 degraded or dwarfed sub-order. Now, the tropical 

 Rubiaccic have tubular blossoms with long throats, and as 

 a rule with five lobes to the corolla ; but many of the SteL- 

 lates have lost the tube and one corolla lobe. S/terardia 

 arvensis, which has departed least of our British species 

 from the norma of the race, has a distinct tube to the 

 corolla, and is blue or pink. Asperula, which approaches 

 nearer to the retrograde Galiums, has one pale lilac 

 species and one white. The Galiums have no corolla-tube 

 at all, and most of them are white ; but two British 

 species, G. verum and G. cruciata, are yellow, and one of 

 these has become practically bi-sexual— a common mark 

 of Retrogression. Rubia peregrina is even green. This 

 clearly marked instance of Retrogression from blue 

 through lilac and white to yellow makes the case of the 

 Composites easier to understand. No doubt the dwarfed 

 northern Stellates have found that they succeeded better 

 by adapting themselves to the numerous small insects of 

 the fields and hedgerows, and therefore have fallen back 

 upon the neutral colours, white and yellow. 



After so many instances of more or less probable Re- 

 trogression, it will not surprise us to learn that in an 

 immense number of other cases there is good reason to 

 suspect some small amount of dwarfing or even Degene- 

 ration. It may have struck the reader, for example, 

 when we were dealing with the Crucifers, that many of 

 the smaller white forms were apparently lower in type 

 than large and brilliant yellow flowers like the charlocks. 

 That is quite true ; but then, many of these small types 

 are demonstrably dwarfed and slightly degraded, as, for 

 example, Cardamine hirsuta, which has usually only four 

 stamens instead of six, thus losing the most characteristic 

 mark of its family. In Senebiera didyma, the petals have 

 generally become quite obsolete ; in some species of 

 Lepidwm, Arabis, Draba, &c, they are inconspicuous 

 and often wanting. So in the smaller Alsinca: there are 

 many signs of Degeneration. The normal forms of 

 Caryophyllacea have two whorls of five stamens each ; 

 but these little creeping or weedy forms have often only 

 one whorl, as in Holosteum, some Cerastiums, the smaller 

 Slellarias, Spergula, Poly car pon, &c. In Sagina, Cher- 

 let ia, and other very small types, the petals are often or 

 always wanting. Indeed, most botanists will probably 

 allow that nearly all our minute-flowered species, such as 

 Montia fontana, Claytonia perfoliaia, Elatine hexandra, 

 Rsthnia Mill grana- Circa j lut-jt-.-w-v.l '/■{ -.ig'.-t palusit is, 

 Peplis Portula, Tillaa muscosa, Myriophyllum spicatum, 

 Hippurus vulgaris, Centuiiculus minimus, and Cicendia 

 pusilla, are distinctly degenerate forms. Though ob- 

 viously descended from petaliferous ancestors, and closely 

 allied with petaliferous genera or species, many of them 

 have lost their petals altogether, while others have them 

 extremely reduced in size. In several cases, too, the 

 number of sepals, petals, or stamens has been lessened, 

 and the plant as a whole has suffered structural degrada- 

 tions. Most of these dwarfed and degenerate flowers, if 

 they have petals at all, have them white or very pale pink. 



Readers of Sir John Lubbock's admirable little book 

 on " British Wild-Flowers in Relation to Insects" will 

 readily understand the reason for this change. They will 

 remember that white flowers, as a rule, appeal to an ex- 

 ceptionally large circle of insect visitors, mostly of small 

 and low grades. Hence, some among these very small 

 flowers may often succeed, in certain positions, better 

 than larger ones. Moreover, they will recollect that in 



