A TYPE OF PALEOZOIC PLANTS. 405 



genera. Several are commonly regarded as distinctly 

 calamitean in affinity, but it is nearly always impossible to 

 speak definitely as to the nature of the plant to which they 

 belonged. x One of these cones has been known for some 

 time as Calamostachys Binneyana Schimp. A recent re- 

 examination of this species, in which the histological struc- 

 ture is very clearly present, has led Hick, 2 and Scott and 

 Williamson to the conclusion that it is most probably a 

 strobilus of some form of Calamites, thus confirming the 

 views expressed by Carruthers in 1867. Its structure may 

 be brieflv summarised as follows : a slender axis traversed 

 by a stele consisting of a pith surrounded by a ring of 

 bundles, the persistent central tissue consisting of thick- 

 walled cells in the peripheral portion, and thinner-walled 

 elements in the centre. In some cases the central cylinder 

 is triangular in form, in others quadrangular. The position 

 of the protoxylem elements is marked by somewhat irregular 

 spaces ; the bundles are of the collateral type, and frequently 

 secondary fascicular and interfascicular xylem has been 

 added to the primary bundles. The cortical tissue consists 

 of thick-walled cells towards the periphery, and more delicate 

 cells internally. Attached to this central axis, which it 

 should be noted shows a distinct calamitean type of struc- 

 ture at the nodes, there are numerous alternating whorls of 

 sterile and fertile lateral appendages, the former being 

 spoken of as bracts, the latter as sporangiophores. Each 

 whorl of bracts is made up of about twelve segments ad- 

 herent basally in the form of a disk, which is split up at its 

 margin into separate linear- segments turned sharply up- 

 wards at right angles to the undivided basal portion. Each 

 linear segment is traversed by a small vascular strand. The 

 sporangiophores forming the fertile verticils are usually half 

 as numerous as the bracts ; each consists of a pedicel, 

 terminating distally in a peltate expansion, and bearing four 

 sporangia containing numerous spores, often grouped to- 

 gether in tetrads. This form of cone appears to be always 

 homosporous. Each pedicel contains a single bundle, 



1 Weiss (1). - Hick (1). 



