138 THEORY OF THE STROBILUS 



place to the axis in the initial differentiation of the shoot. Perhaps the 

 most explicit statement on this point is that by Alexander Braun, who 

 remarks in his Rejuvenescence in Nature (English edition, p. 107), 

 referring to phytonic theories, that "all these attempts to compose the 

 plant of leaves are wrecked upon the fact of the existence of the stem as 

 an original, independent and connected structure, the more or less distinct 

 articulation of which certainly depends upon the leaf-formation, but the 

 first formation of which precedes that of the leaves." Unger also, in his 

 botanical letters to a friend (No. VIII.), described how "The first endeavour 

 is directed towards the building up with cell-elements of an axis" "those 

 variously formed supplementary organs which are termed leaves originate 

 laterally upon it " and he concludes that " we may [therefore] say with 

 perfect justice that the plant ... is, as regards form, essentially a system 

 of axes." Naegeli contemplated a somewhat similar origin of the leafy 

 shoot as an alternative possibility ; in fact, that the apex of a sporogonium- 

 like body elongated directly into that of the leafy stem, in which case 

 the axis would be the persistent and prominent part, and the leaves be 

 from the first subsidiary, and lateral appendages. In my theory of the 

 strobilus in Archegoniate Plants the central idea was somewhat similar 

 to this. 1 It may be briefly stated thus : There seems good reason to hold 

 that a body of radial construction, having distinction of apex and base, 

 and localised apical growth as its leading characters, existed prior to the 

 development of lateral appendages in the sporophyte ; the prior existence 

 of the axis and lateral origin of the appendages upon it are general for 

 normal leafy shoots. The view thus put forward is, indeed, the mere 

 reading of the story of the evolution of leaves in terms of their normal 

 individual development. 



It is natural to look to the Pteridophytes for guidance as to the origin 

 of foliar development in the sporophyte, for they are undoubtedly the most 

 primitive plants with leafy shoots. They may be disposed according 

 to the prevalent size of their leaves in a series, leading from microphyllous 

 to megaphyllous types. I have lately shown that such a seriation is not 

 according to one feature only, but that certain other characters which 

 have been summarised as " Filicineous " tend to follow with the increasing 

 prominence of the leaf. 2 This indicates that such seriation is a natural 

 arrangement. Now it is possible to hold either that the large-leaved 

 Fern-like plants were the more primitive, and the smaller-leaved, derivatives 

 from them by reduction ; or, conversely, that the smaller-leaved were the 

 more primitive, and the larger-leaved derivatives from them by leaf- 

 enlargement ; other alternative opinions are also possible, such as that 

 the leaf-origin has been divergent from some middle type, or that the 

 leaves of Vascular Plants may have been of polyphyletic origin. For the 

 moment we shall leave these latter alternatives aside. 



Much of the difference of view as to foliar origin centres round the 

 ^Annals of Botany, vol. viii., p. 343. ^Studies, v., p. 254. 



