SPHENOPSIDA 103 



the appearance of having been formed in separate strands, 

 although in fact it was formed from a continuous vascular 

 cambium. 



Protocalamostachys is the name given to a peculiar cone 

 described by Walton^^^ from Lower Carboniferous rocks in 

 the Island of Arran. Two small pieces of the cone had 

 dropped into the hollow stump of a Lepidophloios before it 

 became petrified. Unhke the cones of other members of the 

 Calamitales, its sporangiophores branched twice (Fig. 16D), 

 instead of being peltate. In this respect, it showed some 

 affinities with the Sphenophyllales and also with the 

 Hyeniales. However, Walton compares it most closely with 

 Pothocites, a cone associated with leaves of the Astero- 

 calamites type. Furthermore, within the axis of the cone 

 there is centripetal primary wood as in the stem of Proto- 

 calamites. 



The height to which Calamites grew is difficult to deter- 

 mine, because of the fragmentary nature of the remains, but 

 it is almost certain that some specimens must have attained 

 a height of 30 m with hollow trunks whose internal diameter 

 was up to 30 cm. Strictly speaking, the generic name 

 Calamites should be applied only to pith casts of stems and 

 branches, while petrified wood should be described under 



E, reconstruction of Eiicalamites type. Annularia: F. Astero- 

 phyllites: G. Calamites {= Arthropitys): H, part of internodal 

 vascular system. Palaeostachya: i, sporangiophore and bract. 

 Calamostachys : J, part of cone in l.s. Eqiiisetum pratense: K, 

 plant with young sterile shoot; l, young fertile shoot with cone; 

 M, sporangiophore; n, spore with elaters; o, nodal vascular 

 arrangement (1, internodal bundles; 2, leaf trace; 3, branch 

 traces); p, antherozoid. Eqiiisetum sylvaticiim: Q, internodal 

 vascular bundle (4, carinal canal with remains of protoxylem). 

 Archegonium: r (E. hyemale). Embryo: s (E. arvense) (f, foot; 

 1, leaf primordia; r, root primordium; x, stem apex) 



(a, after Stur; b, Renault; d, Walton; e, Hirmer; f, g, Abbott; 

 I, Baxter; J, Scott; k, l, Duval-Jouve; n, Foster and Gifford; 

 o, Fames; p, Sharp; r, Jeff'rey; s, Sadebeck) 



