NATURE 



[July 27, 18N • 



while it is difficult to understand how they could have 

 taken their origin from ordinary leaves— a process of 

 which, if it ever took place, no hint now remains to us. 



In a few rare instances, petals even now show a slight 

 tendency to revert to the condition of fertile stamens. In 

 Monandra fistulosa the lower lip is sometimes prolonged 

 into a filament bearing an anther : and the petals of shep- 

 herd's-purse (Capsella bursa-pastoris) have been observed 

 antheriferous. 



But if the earliest petals were derived from flattened 

 stamens, it would naturally follow that they would be for 

 the most part yellow in colour, like the stamens from 

 which they took their origin. How, then, did some of 

 them afterwards come to be white, orange, red, purple, 

 lilac, or blue ? 



The different hues assumed by petals are all, as it were, 

 laid up beforehand in the tissues of the plant, ready to be 

 brought out at a moment's notice. And all flowers, as 

 we know, easily sport a little in colour. But the question 

 is, do their changes tend to follow any regular and definite 

 order? Is there any reason to believe that the modifica- 

 tion runs from any one colour towards any other ? Appa- 

 rently, there is. All flowers, it would seem, were in their 

 earliest form yellow ; then some of them became white ; 

 after that, a few of them grew to be red or purple ; and, 

 finally, a comparatively small number acquired various 

 shades of lilac, mauve, violet, or blue. 



Some hints of a progressive law in the direction of a 

 colour-change from yellow to blue are sometimes afforded 

 us even by the successive stages of a single flower. For 

 example, one of our common little English forget-me- 

 nots, Myosotis versicolor, is pale yellow when it first 

 opens ; but as it grows older, it becomes faintly pinkish, 

 and ends by being blue like the others of its race. Now, 

 this sort of colour-change is by no means uncommon ; 

 and in almost all known cases it is always in the same 

 direction, from yellow or white, through pink, orange, or 

 red, to purple or blue. Thus, one of the wall- flowers, 

 Cheiranthus chamceleo, has at first a whitish flower, then 

 a citron-yellow, and finally emerges into red or violet. 

 The petals of Stylidium fruticosuin are pale yellow to 

 begin with, and afterwards become light rose-coloured. 

 An evening primrose, Oenothera tetraptera, has white 

 flowers in its first stage, and red ones at a later period of 

 development. Cobaa scandens goes from white to violet ; 

 Hibiscus mutabilis fromwhitethroughflesh-coloured.to red. 

 The common Virginia stock of our gardens (Malcol/nia) 

 often opens of a pale yellowish green ; then becomes 

 faintly pink; afterwards deepens into bright red; and 

 fades away at last into mauve or blue. Fritz Miiller 

 noticed in South America a Lantana, which is yellow on 

 its first day, orange on the second, and purple on the 

 third. The whole family of Boraginacea begin by being 

 pink, and end by being blue. In all these and many 

 other cases the general direction of the changes is the 

 same. They are usually set down as due to varying de- 

 grees of oxidation in the pigmentary matter. 



If this be so, there is a good reason why bees should 

 be specially fond of blue, and why blue flowers should 

 be specially adapted for fertilisation by their aid. For 

 bees and butterflies are the most highly adapted of all 

 insects to honey-seeking and flower-feeding. They have 

 themselves on their side undergone the largest amount of 

 specialisation for that particular function. And if the 

 more specialised and modified flowers, which gradually 

 fitted their forms and the position of their honey-glands 

 to the forms of the bees or butterflies, showed a natural 

 tendency to pass from yellow through pink and red to 

 purple and blue, it would follow that the insects which 

 were being evolved side by side with them, and which 

 were aiding at the same time in their evolution, would 

 grow to recognise these developed colours as the visible 

 ymbols of those flowers from which they could obtain 

 •he largest amount of honey with the least possible 



trouble. Thus it would finally result that the ordinary 

 unspecialisei 1 flowers, which depended upon small insect 

 riff-raff, would be mostly left yellow or white ; those which 

 appealed to rather higher insects would become pink or 

 red ; and those which laid themselves out for bees and 

 butterflies would grow for the most part to be purple or 

 blue. 



Now, this is very much what we actually find to be the 

 case in nature. The simplest and earliest flowers are 

 those with regular, symmetrical open cups, like the 

 Ranunculus genus, the Potentillas, and the Alsinetz or 

 chickweeds, which can be visited by any insects whatso- 

 ever : and these are in large part yellow or white. A 

 little higher are flowers, like the campions or Silence?, 

 and the stocks (Mall/iioia), with more or less closed c >ps, 

 whose honey can only be reached by more specialised 

 insects; and these are oftener pink or reddish. More 

 profoundly modified are those irregular one-sided flowers, 

 like the violets, peas, and orchids, which have assumed 

 special shapes to accommodate bees or other specific 

 honey-seekers ; aud these are often purple and not infre- 

 quently blue. Highly specialised in another way are the 

 flowers like harebells {Campanula), scabious {Dipsacece). 

 and heaths (Ericacca), whose petals have all coalesced 

 into a tubular corolla ; and these might almost be said to 

 be usually purple or blue. And, finally, highest of all 

 are the flowers, like labiates (rosemary, Salvia, &c.) and 

 speedwells {Veronica,) whose tubular corolla has been 

 turned to one side, thus combining the united petals with 

 the irregular shape ; and these are almost invariably 

 purple or blue. 



The very earliest types of angiospermous flowers no* 

 remaining are those in which the carpels still exist in a 

 separate fofm, instead of being united into a single com- 

 pound ovary. Among Dicotyledons, the families, some 

 of whose members best represent this primitive stage, are 

 the Rosacea and Ranunculacece ; among Monocotyledons, 

 the Alisinacear. We may conveniently begin with the 

 first group. 



The roses form a most instructive family. As a whole 

 they are not very highly developed flowers, since all of 

 them have simple, open, symmetrical blossoms, generally 

 with five distinct petals. But of all the rose tribe, the 

 Potentillea, or cinquefoil group, seem to make up the 

 most central, simple, and primitive members. They are 

 simple low, creeping weeds, and their flowers are of the 

 earliest symmetrical pattern, without any specialisation of 

 form, or any peculiar adaptation to insect visitors. Now 

 among the potentilla group, nearly all the blossoms have 

 yellow petals, and also the filaments of the stamens 

 yellow, as is likewise the case with the other early allied 

 forms, such as agrimony {Agrimonia Kupatoria), and 

 herb-bennet {Gcum iirbanum). Among our common 

 yellow species are Potentilla reptans (cii quefoil), P. 

 lorincntilla, P. argentea, P. vcrna, P.fruticosa, and P. 

 anserina. Almost the only white potentillas in England 

 are the barren strawberry (P. fragariastrum\ and the 

 true strawberry {Fragaria vesca), which have, in many 

 ways, diverged more than any other sfecies from the 

 norma of the race. Water-avens {Geum rivale), how- 

 ever, a close relative of herb-bennet, has a dusky purplish 

 tinge ; and Sir John Lubbock notes that it secretes honey, 

 and is far oftener visited by insects than its kinsman. 

 The bramble tribe {Rubecc), including the blackberry (Fig. 

 3), raspberry, and dewberry, have much larger flowers than 

 the potentillas, and are very greatly frequented by winged 

 visitors. Their petals are usually pure white, often with 

 a pinky tinge, especially on big, well-grown blossoms. 

 One step higher, the cherries and apples (though geneti- 

 cally unconnected), have very large and expanded petals 

 (Fig. 4), white toward the centre, but blushing at the 

 edges into rosy pink or bright red. Finally, the true 

 roses (Fig. 5), whose flowers are the most developed of 

 all, have usually broad pink petals (like those of our own 



