)I0 



A TEXTBOOK OF THEORETICAL BOTANY 



structure is a bifid sporophyll, bearing a synangium or plurilocular sporangium, 

 a view which tends to bring the plant into line with Lycopodium. Secondly, 

 that the whole sporangium-bearing structure is a short fertile axis, a spor- 

 angiophore, terminating in a synangium and bearing two leaves or bracts. 

 If the latter be the case these sporangiophores are not lateral branches in the 

 usual sense, since they have no subtending leaf and they must therefore be 

 regarded as reduced limbs of successive apical dichotomies of the main axis. 



Fig. 619. — Psilotiun trique- 

 trum. Complete plant 

 showing branched rhi- 

 zome and shoots bear- 

 ing sporangia. Much 

 reduced. 



Fig. 620. — Psilotuni trique- 

 triini. Portion of a 

 branch bearing synan- 

 gia. Below the middle 

 synangium may be seen 

 the two cusps of the 

 bifid leaf. 



Although the first view is the simpler the objections to it are twofold. 

 Nowhere else is there a case of a sporophyll bearing a synangium on its 

 adaxial face. Secondly the so-called sporophyll receives no vascular trace 

 from the stem while the synangium does, a fact which speaks strongly for 

 its axial nature. Comparison with Tmesipteris helps to confirm the sporangio- 

 phoric theory, which may be accepted as the more probable (Fig. 621). If 

 it be accepted it falls into line with the ancient Psilophytales in which one 

 branch of each dichotomy of the axis is fertile with a terminal sporangium, 

 while the other remains sterile. The trilocular condition in the sporangium 



