82 Sykes . — The Anatomy and Morphology of Tmesipteris. 
in the presence of the third bundle supplying the synangium, 1 which may 
represent the vascular supply of the apex of the synangial branch. The 
presence of a third bundle in the sterile branches 2 may perhaps be also of 
interest in this connexion. 
Strasburger 3 , in his paper of 1873, considered the axial nature of the 
sporophyll in the Psilotaceae to be so obvious that he carried his arguments 
further, and suggested that the sporangium in the Lycopods is also 
primitively an axial organ which has become associated with the sporophyll 
in the course of evolution. 
It seems very probable that the distinction so generally drawn between 
foliar and axial organs may prove to be somewhat forced, and it is especially 
among the lower Pteridophyta that we should expect to find it less sharp ; 
indeed, according to views recently expressed by Tansley 4 , we are to look 
upon a leaf as a specialized branch derived from an ultimate ramification 
of the primitive thallus. Inasmuch, however, as the general idea of a leaf 
is concerned, it is certainly a flattened lateral emergence, capable of limited 
growth, while a branch is a non-flattened emergence which grows apically 
for a considerably greater period of time. The sporangial branch of 
Tmesipteris appears to belong to the latter of these two categories, and 
the sporangiophore bearing the synangium seems to be the transformed 
apex of a branch. Text-fig. VII, p. 72, is a case in which a pedicel with its 
synangium terminates the main axis ; and its position makes it difficult to 
regard this sporangiophore as foliar, though it might be looked upon as an 
organ sui generis . 5 The close association of the sporophylls with the 
synangium need not necessarily be a primitive character, and it may well 
have been that a scattered arrangement of the reproductive and assimilating 
members prevailed in some of the ancestral strobili. There are obvious 
advantages in a connexion between those vascular elements which bring 
elaborated food products from the assimilating tissues and those which 
supply the developing spores. Such a connexion of the vascular systems 
of bract and sporangiophore is seen in Calamostachysl and has been 
interpreted as indicating that the arrangement in that cone is derived from 
one in which a sporangiophore was found in the axil of a bract, as in Palaeo- 
stachya. But recent unpublished investigations of Mr. Hickling’s, quoted 
by Scott 7 , have shown that in Palaeostachya the trace supplying the 
sporangiophore pursues a very remarkable course ; while arising from the 
trace of the bract in the axil of which the sporangiophore is found, it runs 
vertically for some distance up the stem, and then sharply bends ‘ back- 
1 See above, pp. 73-4. 3 Bertrand, 1 . c., Figs. 243-246. 
3 Strasburger, B. Z., 1873. 1 Tansley, 1907. 
5 Bovver, 1903, p. 192. 6 Renault, 1896, pp. 130-4, 
7 Scott, 1907, pp. 159-60. Note. — Since the above was written, Mr. Hickling’s paper has 
appeared; Ann. of Bot. 1907. See esp. Text Fig. r. 
