FOSSIL PLANTS OF THE CAEBONIFEROUS SYSTEM. 



737 



medulla penetrated this cylinder by a series of -wedges, whicli were 

 continued to the outer portion of the stem by their cellular laminse. 

 The appendicular organs (leaves) were produced in whorls. Williamson 

 considers the structure of the medullary and ligneous zones as resembling 

 that of the stem of an exogen of the first year. On making a longi- 



kii'jW. 



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mm 



Pig. 916. 



Fig. 917. 



tudinal tangential section of the stem, the woody zones show alter- 

 nating parallel bands of vascular and cellular tissue. The bark con- 

 sists of a thin layer of parenchyma. It is smooth outside, and does 

 not present ridges or furrows. The ligneous cylinder of Calamite, as 

 it increases in size and age, exhibits less and less of the Calamitean 

 peculiarities seen in young stems ; the external part becoming unsul- 

 cated. In a Calamitean plant, called by Williamson Calamopitus, 

 canals pass from the medullary cavity, horizontally to the bark, 

 below the nodes (infra-nodal). Calamites give off subterranean 

 branches from rhizomes as well as slender appendages from the 

 aerial stem, arranged in verticUs at the nodes. Williamson puts 

 Oalamites in his order Calamitacese, allied to Equisetacese, but differing 

 in having cryptogamic reproduction connected with an exogenous de- 

 velopment of the stem. Schimper considers Oalamites as having an 

 analogy with Equisetum in their fructification. He regards them as 

 fossU Equisetacese. Annularia and SphenophyUum are considered as 

 establishing a passage from the Equisetacese to the Lycopodiacese. 

 Some gigantic fossU Equiseta had a diameter of more than 12 centi- 

 metres, and a height of 8 to 10 metres. The branches, which adorned 

 the higher part of them in the form of a crown, are simple, have at 

 their extremity a spike of the size of a pigeon's egg, and are organised 

 exactly like the spikes of living Equiseta. There is also a resem- 

 blance between them as regards their rhizomes. Dr. W. E. M'Nab 

 has examined the Equisetum stem, and contrasted it with that of Cala- 

 mite, and he has come to the following conclusions : — That the stem 

 of Eqidsetums differs but little in construction from that of Calamites : 



Kg. 916. Calamites Suckovdi, composed of jointed striated fragments having a bark. 

 Kg. 917. Calamites cannaeformis, giving off roots. 



3 B 



