BY THE REV. J. E. TENISON-WOODS, F.G.S., F.L.S. 63 



In some families the costa is central, and in others it is not in 

 the centre and is called lateral. 



Evanescent. — Not reaching the apex or margin. 



Equisetin^e. 



The plants which compose this class (says Schimper) are only at 

 present represented by one genns, that of the Equisetums or Horse- 

 tails, which itself is not directly related to any other type of 

 vascular cryptogams. There exists but one genus in the present 

 day with only a few species, which are united together by very 

 concise characters, and they do not pass by any degrees into any 

 other genus. These plants play a very insignificant part in the 

 world's vegetation just now, but in the coal period and lower 

 mesozoic it was not so. Both in species and individuals the 

 Equisetacese played a most important part. Tn fact the great mass 

 of the coal is supposed to have been formed by them. 



The fossils are divided into two orders, the Equisetacese and the 

 Calamitese. The former is thus defined : herbaceous or arborescent 

 plants ; stems rising from an underground articulate branched 

 rooting rhizome, nearly always fistular. Rhizome — underground, 

 jointed, branched, rooting. Stems— jointed, nearly always hollow. 

 Joints — separated by a diaphragm. Leaves — connate into a sheath, 

 rarely separate at the ends, forming a cylindrical covering often 

 grooved lengthwise, externally permeated by a double series of 

 alternating lacunae. Branches arising beneath the base of the 

 verticillate sheath, simple, in whorls, or wanting. Reproductive 

 organs — arising from a lobed fugacious prothallus. Fructification 

 — in a terminal spike. Receptacles pedicillate, verticillate under 

 hexagonal shields. Sporangia — in groups round the perpendicular 

 pedicels, opening laterally. 



The greatest development of this family is in the Carboniferous 

 and Permian formations. There it is represented by a great 

 number of genera and species which have no forms at all like 

 them in the present vegetation, such as Catamites, Asterophyllites 



