FLORA OF THE PALEOZOIC PERIOD. 



29 



continue to multiply, and bear fructification at their bases. 

 They have both large and small spores. 



Fig. 11, a. 



Fig. 11, h. 



Fig. 12. 



Another important order of vascular Acrogens is the Equi- 

 setacea3 or Horse-tails (Fig. 18). These are Cryptogams, 

 having rhizomes, bearing hollow, striated branches, which 

 secrete in their epidermis a considerable amount of silex. 

 These branches are jointed and have membranous sheaths at 

 the articulations, which are whorls of leaves reduced to a very 

 rudimentary condition. The fructification consists of cone- 

 like bodies (Fig. 18, /) bearing peltate polygonal scales, 

 under which are spore-cases (Fig. 19), enclosing spores with 



Fig. 11, a. Bifurcating (forked or dichotomous) trunk (caudex) of 

 a Tree-fern (Alsophila Perrottetiana), showing the scars (cicatrices) left 

 by the fallen fronds. These scars exhibit the arrangement of the vas- 

 cular bundles. Fig. 11, b. Rhizome of Lastrea Filix-mas (male fern), 

 showing scars of the leaves, c, with markings of the vascular bundles. 



Fig. 12. Transverse section of the stem (caudex) of a Tree-fern 

 (Cyathea), showing the arrangement of the celhilar and vascular tissue. 

 The cellular tissue of the centre, m ; that of the circumference, p ; 

 vascular cylinder, / v, consisting of dark-coloured pleurenchyma or 

 ligneous tubes, /, and paler vessels, v, chiefly scalariform and closed 

 spiral, and pierced by the meshes for the leaf-bundles at m ; the outer 

 cortical portion connected with the bases of the leaves, e. 



