3°o 



NATURE 



\July 27, 1882 



the reasons for this belief. For if the petals were origin- 

 ally a row of altered stamens set apart for the special 

 function of attracting insects, it would be natural and ob- 

 vious why they should begin by being yellow ; but if they 

 were originally a set of leaves, which became thinner and 

 more brightly coloured for the same purpose, it would be 

 difficult to see why they should first have assumed any 

 one colour rather than another. 



The accepted doctrine as to the nature of petals is that 



Fig. i. — Transition from 



to petals in the white water lily. 



discovered by Wolf and subsequently rediscovered by 

 Goethe, who held that all the parts of the flower were 

 really modified leaves, and that a gradual transition could 

 be traced between them, from the ordinary leaf, through 

 the stem-leaf and the bract, to the sepal, the petal, the 

 stamen, and the carpel. Now, if we look at most 

 modern flowers, such a transition can undoubtedly be ob- 

 served ; and sometimes it is very delicately graduated, so 



-Transition from 



pal (,) in fl. 



that you can hardly say where each sort of leaf merges 

 into the next. But, unfortunately for the truth of the 

 theory as ordinarily understood, we now know that in the 

 earliest flowers there were no petals or sepals, but that 

 primitive flowering plants had simply leaves on the one 

 hand, and stimens and ovules on the other. The oldest 

 types of flowers at present surviving, are certain gymno- 

 sperms, such as the cjcads, of which the well-known 



Fig. 3. — Vertical 



Zamias of our conservatories may be regarded as good 

 examples. These have only naked ovules on the one 

 hand, and clusters of stamens in a sort of cone on the 

 other. The gymnosperms are geologically earlier than 

 any other flowering plants. But, if petals and sepals are 

 later in origin than stamens and carpels, we can hardly 

 say that they mark the transition from one form to the 

 other, any more than we can say that Gothic architecture 



marks the transition from the Egyptian style to the 

 classical Greek. It is not denied, indeed, that the stamen 

 and the ovary are themselves by .origin modified leaves — 

 that part of the Wolfian theory is absolutely irrefutable — 

 but with the light shed upon the subject by the modern 

 doctrine of evolution, we can no longer regard petals and 

 sepals as intermediate stages between the two. The 

 earliest flowering plants had true leaves on the one hand, 



of apple blossom (pinky white). 



and specialised pollen-bearing or ovule-bearing leaves on 

 the other hand, which latter are what in their developed 

 forms we call stamens and carpels ; but they certainly had 

 no petals at all, and the petals of modern flowers have 

 been produced at some later period. 



All stamens show a great tendency easily to become 

 petaloid, that is to say, to flatten out their filament, and 

 finally to lose their anthers. In the waterlilies we can 



of dog-rose (bright piik). 



trace a regular gradation from the perfect stamen to the per- 

 fect petal. Take for example our common English white 

 Nymplia-a alba (Fig. 1 ). In the centre of the flower we find 

 stamens of the ordinary sort, with rounded filaments, and 

 long yellow anthers ; then, as we move outward, we find 

 the filaments growing flatter and broader, and the anthers 

 less and less perfect ; next we find a few stamens which 

 look exactly like petals, only that they have two abortive 



Fig. 6. — Vertical section of buttercup (pri 



anthers stuck awkwardly on to their summits ; and, 

 finally, we find true petals, broad and flat, and without 

 any trace of the anthers at all. Here in this very ancient 

 though largely modified flower we have stereotyped for 

 us, as it were, the mode in which stamens first developed 

 into petals, under stress of insect selection. 



"But how do we know," it maybe asked, "that the 



