INTRODUCTION. MORPHOLOGY AND ORGANOGRAPHY ir 



history in the formation of organs. There are many experimental 

 proofs of this furnished partly by nature itself, partly through artificial 

 methods, of which some mention must now be made. If the flower- 

 buds of Knautia arvensis are attacked by the fungus Peronospora 

 violacea, the staminal primordia commonly develop into petals. These 

 primordia were not however ' indifferent.' The series of processes through 

 which they would become stamens had already begun when the attack 

 of the fungus turned the development in another direction. Other 

 similar examples will be found in the section upon malformations ; 

 I will only mention here that, as my investigations have proved, a simple 

 disturbance may hinder the transformation of the primordia of foliage- 

 leaves into scale-leaves, and, as the case of Onoclea Struthiopteris shows, 

 a transformation to sporophylls may be likewise prevented 1 . To this 

 instance I may refer further here. The sporangia of ferns arise on 

 leaves which are termed sporophylls. These are either quite like the 

 foliage-leaves, as is the case in Aspidium Filix-mas, or the formation 

 of sporangia causes more or less profound changes in the form, direction, 

 and structure, of the sporophyll. Onoclea Struthiopteris belongs to that 

 group of ferns in which such differences are the greatest ; and its 

 sporophylls are produced in regular alternation with the foliage-leaves. 

 For a considerable time their development conforms with that of the 

 primordia of the foliage-leaves, it is only when the formation of sporangia 

 sets in. that a modification in its course is observed. If now all the 

 foliage-leaves be removed from the plant the development of sporophylls 

 is hindered ; the primordia of the sporophylls, which are nothing else 

 than primordia of foliage-leaves, are then forced to develop into foliage- 

 leaves and the production of sporangia is either partially or entirely 

 suppressed. From the point of view also of inheritance, by which we 

 mean the repetition in descendants of their ancestral development apart 

 from small deviations, it is of importance that only definite organ- 

 primordia need to be transmitted, and out of their transformation others 

 then proceed ; only the causes of such transformation are not, as in the 

 example of Knautia above referred to, external, but internal they belong 

 to the capacity of the plant itself. 



Our idea of metamorphosis is then primarily an ontogenetic one 

 and is therefore capable of experimental measurement and proof. 

 Phylogenetic considerations may come in, but the incorrectness of speaking 

 of a metamorphosis purely in a phylogenetic sense is shown by this 

 simple fact that the doctrine of metamorphosis is older than the theory 

 of descent, and would remain even if the latter were given up. 



' Goebel, Uber kunstliche Vergrunung der Sporophylle von Onoclea Struthiopteris, lloffm., in 

 Ber. d. deutschen botan. Gesellsch. Bd. v (1887), p. Ixix. 



