120 SCIENCE PROGRESS. 



sporophylls of ferns, in which the foliage leaves often are 

 strikingly distinct from those which bear the sporangia. It 

 is possible, experimentally, to compel the sporophylls of 

 Onoclea Struthiopteris to develop as foliage leaves. The 

 investigation of the young stages shows that up to a certain 

 period of their life the two structures are quite indistin- 

 guishable, and it is only subsequently, and owing to the 

 nutritional changes connected with the appearance of their 

 sporagia, that the sporophylls depart from the form ex- 

 hibited by the rest of the leaves of the plant. This correla- 

 tion between sporangia! formation and the shape of the leaf 

 (which, however, is not equally distinct in all ferns) is also 

 admitted by Bower ; he believes, however, on phylogenetic 

 grounds, that the conclusion here arrived at should be 

 reversed, and that the foliage leaves ought rather to be 

 regarded as metamorphosed sterile sporophylls. But in my 

 opinion, Botany, as a science, is more concerned with facts 

 of experience than with phylogenetic theories. Experience 

 shows that in all ferns foliage leaves are the first to appear, 

 and that these may subsequently become altered, so as to 

 form sporophylls. As to what occurred in prehistoric ages, 

 we require far more convincing proofs than are afforded by 

 the materials at present within our reach, before we can 

 speak with any assurance. Meanwhile, one may say with 



Faust : — 



Mein Freund, die Zeiten der Vergangenheit 

 Sind uns ein Buch mit sieben Siegeln. 



And I, for my part, prefer to abide by the evidence actually 

 before us. 



As regards the shoot, there is also experimental evidence 

 forthcoming. Some of this was furnished by T. A. Knight, 1 

 whose services to morphology have often been insufficiently 

 recognised. 



Knight experimented, especially with the potato. The 

 subterranean tubers of this plant are, as is well known, 

 merely altered shoots. Knight, however, succeeded in 



1 Cf. A Selection from the Physiological and Horticultural Papers by 

 Thomas Andrew Knight, London, 1841. Also, Goebel, " Zur geschichte 

 unserer Kentniss d. correlations-vorgange," F/ora, 1893, p. 3S ff. 



