THE SHAPES AND ARRANGEMENTS OF FLOWERS. 611 



of the flowers themselves : they only prove modification in the 

 grouping of the flowers. But beyond snowing, as they do conclu- 

 sively, how readily a bilateral arrangement of flowers is producible 

 out of an arrangement that was not bilateral, by the action of light, 

 etc. ; they give increased probability to the belief that changes in the 

 shapes of flowers are producible by the same agencies. Doubtless 

 this change in the attitudes of the flower-buds is due to the action of 

 light on their calyces and peduncles more than to its action on their 

 unfolding corollas. But along with an action so decided on the growth 

 of these sheathing and supporting organs containing chlorophyl, it is 

 scarcely probable that there is no action on the growth of the petals, 

 containing other colouring matter; considering that in both cases 

 the development of the colouring matter depends on the action of 

 light, and considering also the effect of light on petals, familiarly 

 shown by their opening and closing. And if even but a small 

 effect is producible on the growth of the corolla, then it is to be 

 expected that light will be an agent in changing the form of the 

 corolla, when the attitude of the flower causes its parts to be dif- 

 ferently exposed. For a small effect on the individual flower will 

 become a great effect in the flowers of remote descendants ; pro- 

 vided the changed attitudes of the flowers preserve considerable 

 constancy throughout the succession of individuals. 



Be this as it may, however, the facts I have here described, 

 which I doubt not other observers have seen paralleled in other 

 plants, are instructive, as showing how quickly certain metamor- 

 phoses are produced, and as implying the easy establishment of such 

 metamorphoses as permanent characters in a species, if the modify- 

 ing conditions become permanent. The changes of arrangement 

 I have pointed out, do not become permanent in this species because 

 its individuals are variously affected by the modifying forces : on 

 some they do not act at all, on some a little, on some much ; and 

 even on the same individual the different shoots are quite differently 

 affected. But if the habit of this plant were greatly changed — if, 

 for instance, by spreading into habitats yielding abundant nutri- 

 ment, the plant became very luxuriant, and, multiplying its branches, 

 grew shrub-like ; it is clear that, being shaded by one another, these 

 branches would be habitually circumstanced in a way like that which 

 we here see produces bilateralness in the distribution of the flowers, 

 if not in the flowers themselves ; and being thus permanently 

 affected, would become permanently bilateral. Accumulating by 

 inheritance, what is here only an individual peculiarity, would 

 become a peculiarity of the species — a specific character. 



