LYCOPSIDA 85 



some species have more complicated stelar arrangements. 

 S. Kraussiana, now naturalized in parts of the British Isles, 

 has a creeping habit and has two steles which run side by 

 side (Fig. 14 J), except at the nodes where they interconnect. 

 S. Braunii (Fig. 14E) is one of the many species which have a 

 creeping stem with erect frond-like branch systems: the 

 creeping axis is bi-stelic, with one stele lying vertically above 

 the other, while the erect axes are monostelic. S. Willdenowii 

 is a climbing, or vine-like, species and may have three 

 ribbon shaped steles (Fig. 14L) or even four. The most 

 complex of all is S. Lyallii, where the creeping axis is di- 

 cycHc and the aerial axes are polystelic. The central stele of 

 the creeping axis is a simple ribbon of metaxylem, without 

 any protoxylem, surrounded by phloem, pericycle and endo- 

 dermis. This is surrounded by a cylindrical stele which is 

 amphiphloic (i.e. has phloem to the inside as well as to the 

 outside of the xylem) and is bounded, both externally and 

 internally, by endodermis. Both steles play a part in the 

 origin of the many steles in the aerial axis, which number 

 twelve or thirteen, four of them being main ones to which the 

 leaf traces are connected, while the rest are accessory steles. 

 It is important to realize that, however complex the stem 

 of a mature plant may be, the young sporeUng Selaginella is 

 invariably monostehc, there being a gradual transition along 

 the axis until the adult condition is achieved. This observa- 

 tion has naturally, in the past, led to the supposition that 



Steles : S. selaginoides, h (aerial axis), i (creeping axis) ; 

 S. Kraussiana, j; S. flabellata, k; S. Willdenowii, L. 

 Embryology: S. Martensii, m-p; S. selaginoides, q; 

 S. Poulteri, R, s, t; S. Kraussiana, u, v; 

 S. Galleottii, w ; S. denticulata, x. 

 Biflagellate sperm, y 



(1, ligule; 2, rhizophore; 3, diaphragm; a, archegonial tube; 

 f, foot; r, root; s, suspensor; x, stem apex) 



(a, b, c, f, after Hieronymus; h-l, Gibson; m-x, Bruchmann; v, 

 Dracinschi) 



