ioo SCIENCE PROGRESS. 



slight or altogether absent. Prof. Bower, 1 who has recently 

 urged with great force the claims of the sporophyll 

 to be regarded as the primitive leaf, sees in the differ- 

 entiation of leaves in the Ferns, first of all an increase of the 

 reproductive, spore-bearing area, as compared with the 

 Mosses, by the development of sporophylls ; and then the 

 further evolution of the nutritive functions by the differ- 

 entiation of some of the sporophylls as foliage-leaves. 

 The relative positions of Goebel and of Bower may be 

 summed up in a single sentence : whereas Goebel regards a 

 sporophyll as a foliage-leaf which has become metamor- 

 phosed in consequence of the development of spores from 

 its substance, Bower regards a foliage-leaf as a sporophyll 

 which has lost its primitive form in consequence of sterilisa- 

 tion. The Fern-like plants are the main battle-ground upon 

 which this question is being contested. When the issue 

 is decided there, it will also have been decided for the 

 Flowering-plants (Phanerogamia) ; for whatever is true of 

 the relation between the various forms of leaves in the 

 Fern-like plants, must also be true with regard to their 

 descendants the Flowering-plants. It is, therefore, not 

 necessary to attempt a discussion of the matter as regards 

 Flowering-plants : I will merely mention the significant 

 fact that the flowers of the earliest Flowering-plants (Gym- 

 nosperms) consist entirely of sporophylls, being altogether 

 destitute of petals and sepals, whence the primitive nature 

 of the sporophyll may be fairly inferred. 2 



1 Bower, " A Theory of the Strobilus in Archegoniate Plants," Annals 

 of Botany, viii., p. 343, 1894 : " Studies in the Morphology of Spore-pro- 

 ducing Members— Equisetineae and Lycopodineae," Phil. Trans. Roy. Soc, 

 vol. 185 B, 1894, p. 473. Some interesting facts supporting Prof. Bower's 

 view have recently been published by Atkinson, The Transformation of 

 Sporophyllary to Vegetative Organs, Boston, 1896. He has found in certain 

 Ferns (Onoclea sensihilis and Onoclea Struthiopteris) which have clearly differ- 

 entiated sporophylls and foliage-leaves, that if the young foliage-leaves be 

 destroyed early in the season, the sporophylls (which develop later) do not 

 present their characteristic form, but more or less resemble the foliage- 

 leaves and are partly or completely sterile. These observations show that 

 when nutritive functions are, as it were, forced upon sporophylls, they 

 assume the habit of foliage-leaves. 



2 This point is well brought out by Mr. Grant Allen'in his Colours of 



