PROBLEMS OF PLANT MORPHOLOGY 93 



to change scale leaves (cataphylls) and sporophylls into foliage 

 leaves, inflorescences into vegetative shoots, and, vice versa, plagio- 

 tropous into orthotropous shoots, hypogseous into epigaeous, not 

 to mention the interesting results which have been obtained by 

 Klebs l in his studies of the lower plants. 



Let us take, for example, the just mentioned transformations 

 of scale leaves into foliage leaves and of sporophylls into sterile leaves. 

 Here developmental study and experiment immediately encroach 

 on each other. Development has shown that, e. g., the bud- 

 scales of many trees which in their definitive condition are very 

 different from the foliage leaves, yet parallel them developmentally 

 in an extraordinary degree; and that many bud-scales possess the 

 fundament of a leaf-blade w r hich has failed to develop and has thus 

 become vestigial. 2 Similarly, the fundaments of the foliage leaf and 

 the sporophyll in Onoclea 3 are the same up to a quite late stage of 

 development, beyond which each follows its own course. These 

 facts gave occasion to the question whether or not it were possible 

 to influence the development at will, and so to cause a scale leaf or a 

 sporophyll to grow from a fundament which otherwise would develop 

 into a foliage leaf. It has been shown that such transformations may 

 be occasioned in a simple way, and the developmental correspondence 

 makes such a limited transformation without further difficulty cap- 

 able of being understood. And since seedlings produce, apart from 

 the cotyledons and certain adaptations in hypogseous germination, 

 only foliage leaves, which are arranged for the work of photosynthesis; 

 since further it is seen that all foliage leaves of one and the same 

 plant, different as they appear externally, yet in reality follow one 

 and the same course of development, which, as we have seen, is 

 remarked also in scale leaves and sporophylls, 1 accordingly come 

 to the view that other leaf-organs are derived from foliage leaf funda- 

 ments through a change in the course of development occurring at 

 an earlier or later period of growth. This conception has found 

 many opponents, some of them for the reason that they have not 

 been able to free themselves from the purely historical conception 

 of the problem. 



But the historical question cannot help us over the ontogenetic 

 problem, any more than the solution of the latter alone can answer 

 the historical question. Even if it were proved in all cases that sporo- 

 phylls, flower leaves, sepals, etc., are transformed foliage leaves, 

 it would remain undecided that these are phylogenetically older 



1 Klebs, Die Bedingungen der Fortpflanzung bei niederen Algen und Pilzen, Jena, 

 1896. Further, Ueber willkiirliche Entwickelungsanderungen bei Pflanzen, Jena, 

 1903. 



2 Goebel, Beitrage zur Morphologic und Physiologic des Blattes. Botan. Zeitung, 

 1880. 



3 Goebel, Ueber kiinstliche Vergrunung der Sporophylle von Onoclea Struthiopte- 

 ris, Ber. der Deutschen Botan. Gesellschaft, v, 1887, p. Ixix. 



