BOTRVOPTERIDEAE 501 



Ophioglossaceous plant showing secondary thickening. Other axes are 

 known, which are probably of this affinity, such as Tubicaulis, Anachoropteris, 

 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 (Stauropteris) : 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. 1 



The sporangia are known in Botryopteris, Zygopteris, Grammatopteris^ 

 and Stauropteris : the latter genus is now recognised as a member of 

 the Botryopterideae, and it will be taken first. 2 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 1000 for a single sporangium. It was in 



1 Since the above was written the publication of Tansley's Lectures on the Evolution 

 of the Filicinean Vascular System has commenced (New Phytologist, 1907). He advocates 

 a theory of origin of the leaf in Ferns by differentiation of a dichotomous branch-system 

 to conslitute 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 Stauropteris 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. 



2 See Scott, New Phytologist, 1904, p. 18, 1905, p. 114, and 1906, p. 170. 



