ON METAMORPHOSIS IN PLANTS. 119 



to the organ. The actual ontogeny through which it 

 passes depends upon its own material peculiarities, and this 

 is equally true whether we seek to explain the facts in the 

 light of the chemical composition or in the configuration of 

 the material particles. Thus the leaf does not at first acquire 

 its identity at the final stage of its development, for its 

 whole course of growth is normally already predestined. 

 The operation of new forces acting at a suitable time can 

 indeed materially influence the actual form which is finally 

 assumed, and, speaking generally, the extent of the devia- 

 tion effected approximately depends upon the time of the 

 first effective appearance of this disturbing influence. 



Instances analogous to those already mentioned might 

 be cited in the case of other organs, but for the present it 

 will be sufficient to give an experimental proof of the 

 existence of a real metamorphosis. 



This experiment is performed frequently enough in 

 nature, in the case of many of those phenomena which 

 we term monstrosities. In this place, however, we are 

 more especially concerned with those of which we know the 

 causal agency. When the flower buds of Knautia arvensis 

 are attacked by the fungus known as Peronospora violacea 

 the staminal rudiments develop as petals. The former 

 are bv no means "indifferent" structures. The series of 

 changes which would normally result in the formation of 

 typical stamens may have already begun, but the course of 

 development becomes modified by the action of the fungus. 

 Similarly it was shown by-Peyritsch that from the rudi- 

 ments, perfectly normal rudiments (anlage) of ordinary single 

 flowers, double blossoms may be produced by the action 

 of insects. My own researches have been especially directed 

 to the foliage leaf. I have succeeded in proving that the 

 history of development shows that the bud-scales of our 

 woody plants arise from ordinary leaf rudiments (laubblatt 

 anlagen), and that the deviation from the form of a typical 

 foliage leaf can be prevented by a very simple operation ; 

 so that the structure which, ordinarily, would have assumed 

 the arrested form (scale leaf) will, instead, become a green 

 leaf. And the same is true, mutatis mutandis, for the 



