ORIGIN OF ORGANIC FORMS 293 



The idea that one plant may have arisen from another, 

 an oak from a birch, a rose from a lily, appears so strange 

 at first, that the mind cannot easily grasp it. But is 

 it easier to realise that a cotyledon, a petal, a stamen, 

 a pistil have arisen from a leaf, so dissimilar to them 

 all ? And yet when we discussed the theory of meta- 

 morphosis in our first chapter, we were driven to the 

 conclusion that all these organs so different in form, 

 structure and function, are nevertheless merely the 

 outcome of the transformation of a single organ, the 

 leaf. We arrived at this conclusion on the strength 

 of the following considerations. Firstly, on the ground 

 of the existence of insensible transitions : e.g. we have 

 seen a series of organs in the water lily, neither petals, 

 nor stamens, but similar to both, so that it is quite 

 impossible to say where the one ends and the other 

 begins. The second consideration in favour of the 

 gradual transformation of organs is based upon the 

 monstrosities to be found in plants, i.e. cases in which 

 one organ accidentally acquires the form of another, 

 e.g. when the pistil of a peony assumes the shape of a 

 red petal with ovules at its edges. Cases are most 

 convincing in which such transformation is caused artifi- 

 cially, as for instance in double flowers, where stamens 

 become transformed into additional petals ; as also in 

 experiments, where the outer scales of leaf-buds are 

 transformed into actual leaves. Since these considera- 

 tions force us to admit the possibility of the transforma- 

 tion of one organ into another quite different from it, 

 we are bound to admit more easily still the possibility 

 of such transition between similar organs in different 

 plants. Once we admit that a stamen has arisen from 

 a leaf, we can admit with greater assurance that the 

 leaf of one plant can arise from the leaf of another ; 

 the flower of one plant from that of another. We are 

 forced to do so on the strength of the very considera- 

 tions just brought forward, i.e. on the strength of the 



