68 Variation 



have clearly confirmed Darwin's ideas. The new evening primroses 

 which have sprung in my garden from the old form of Oenothera 

 Lamarckiana, and which have evidently been derived from it, in 

 each case, by a single mutation, do not differ from their parent 

 species in one character only, but in almost all their organs and 

 qualities. Oenothera gigas, for example, has stouter stems and denser 

 foliage; the leaves are larger and broader; its thick flower-buds 

 produce gigantic flowers, but only small fruits with large seeds. 

 Correlative changes of this kind are seen in all my new forms, and 

 they lend support to the view that in the gradual development of 

 highly adapted structures, analogous correlations may have played a 

 large part. They easily explain large deviations from an original 

 type, without requiring the assumption of too many steps. 



Monstrosities, as their name implies, are widely different in 

 character from natural species ; they cannot, therefore, be adduced 

 as evidence in the investigation of the origin of species. There is 

 no doubt that they may have much in common as regards their 

 manner of origin, and that the origin of species, once understood, 

 may lead to a better understanding of the monstrosities. But the 

 reverse is not true, at least not as regards the main lines of develop- 

 ment. Here, it is clear, monstrosities cannot have played a part 

 of any significance. 



Reversions, or atavistic changes, would seem to give a better 

 support to the theory of descent through modifications. These have 

 been of paramount importance on many lines of evolution of the 

 animal as well as of the vegetable kingdom. It is often assumed 

 that monocotyledons are descended from some lower group of 

 dicotyledons, probably allied to that which includes the buttercup 

 family. On this view the monocotyledons must be assumed to have lost 

 the cambium and all its influence on secondary growth, the differentia- 

 tion of the flower into calyx and corolla, the second cotyledon or seed- 

 leaf and several other characters. Losses of characters such as these 

 may have been the result of abrupt changes, but this does not prove 

 that the characters themselves have been produced with equal sudden- 

 ness. On the contrary, Darwin shows very convincingly that a modi- 

 fication may well be developed by a series of steps, and afterwards 

 suddenly disappear. Many monstrosities, such as those represented 

 by twisted stems, furnish direct proofs in support of this view, since 

 they are produced by the loss of one character and this loss implies 

 secondary changes in a large number of other organs and qualities. 



Darwin criticises in detail the hypothesis of great and abrupt 

 changes and comes to the conclusion that it does not give even a 

 shadow of an explanation of the origin of species. It is as improbable 

 as it is unnecessary. 



