BOTRYOPTERIDEAE 501 
Ophioglossaceous plant showing secondary thickening. Other axes are 
known, which are probably of this affinity, such as Zudicaulis, Anachoropterts, 
and <Asterochloena: they show various modifications of the protostelic 
state. From these, as well as from the better known Botryopterideae, it 
is clear that a considerable series of Ferns existed in the Palaeozoic 
period which had a solid protostele, or some slight modification of it: 
their leaf-traces consisted of a single strand, and were given off without 
those profound disturbances of the cauline system characteristic of the 
“phyllosiphonic” type of Jeffrey. 
In Grammatopteris the vascular strand of the petiole was simple in 
outline, as seen in the transverse section. But in other Botryopterids it 
assumed highly complex forms, showing in some cases a tendency to 
radial organisation (Stawroperis): it is upon these that generic distinctions 
have been based. It is unnecessary here to follow out the structural 
details: it suffices to state that the relatively bulky petioles were cylindrical 
in form, and gave off pinnae laterally; while the upper regions have in 
some cases been seen to have the circinate vernation, and to be covered 
while young by a felt of peculiar hairs, as is*the case in the more 
primitive types of modern Ferns.} 
The sporangia are known in Botryopteris, Zygopteris, Grammatopteris, 
and Stauropieris: the latter genus is now recognised as a member of 
the Botryopterideae, and it will be taken first. Its sporangia have been 
found connected with the petiole known as Rachiopteris Oldhamia, Will, 
and are borne terminally on the finest branches of the rachis (Fig. 271). 
Their form is nearly spherical: the wall consisted of a superficial layer of 
larger cells, succeeded internally by several layers of smaller cells: no 
annulus has been observed, and the dehiscence is by a pore at the 
distal end. The spores are numerous: a moderate estimate, based upon 
the sections, would be 500 to rooo for a single sporangium. It was in 
1Since the above was written the publication of Tansley’s Lectures on the Evolution 
of the Filicinean Vascular System has commenced (Mew Phytologist, 1907). He advocates 
a theory of origin of the leaf in Ferns by differentiation of a dichotomous branch-system 
to constitute axis and leaf, and adduces in connection with it many anatomical facts 
relating to the Botryopterideae. It is impossible here to review these facts in detail: 
it may, however, be stated that there appears to me to be nothing in them inconsistent 
with the leaf having been throughout a lateral member. If such a lateral member 
developed to a large size, it is to be anticipated that it should assimilate structurally to 
the axis in its lower parts, as it is seen to do in the Botryopterideae. There is no need 
to assume that it should retain constantly its dorsiventral character: the tendency to radial 
organisation seen in Stauropterts and some others is interesting, but not in any way 
decisive in the absence of all evidence how the leaf actually developed in relation to its 
axis in these ancient forms. Positively, however, we know that in the nearest living 
relatives (Hymenophyllaceae and Osmundaceae) the leaf does originate laterally on the 
axis. The question will be whether surmises based on observation of the mature structure 
in certain imperfectly known fossils are to take precedence of direct observations of 
development in living plants. 
2See Scott, Mew Phytologist, 1904, p. 18, 1905, p. 114, and 1906, p. 170. 
