348 PART IV. CLASSIFICATION. 



are opposite to the xylem-bundles of the stele ; in the Equi- 

 setinse, from the cells forming the inner layer of the two-layered 

 endodermis. 



The stem is generally short and un branched in the Filicinse ; 

 generally elongated and much branched in the Equisetinse and 

 Lycopodinse. 



The leaves are differentiated into foliage-leaves and sporophylls 

 in the Equisetinse and generally in the Lycopodinse, but not in the 

 Filicinse as a rule. The foliage-leaves are relatively large in pro- 

 portion to the stem in the Filicinse, relatively small in the Lyco- 

 podinse, reduced to cataphylls in the Equisetinse. 



The growth in length of root, stem, and leaf, is effected by an 

 apical growing-point : the growing-point has generally a single 

 apical cell in the Filicinse (except root and stem of Marattiacese 

 and Isoetes) and Equisetinse ; in the Lycopodinse (as also in the 

 exceptional Filicinse) there is generally a group of initial cells. 



The anatomy of the stem presents considerable variety. The 

 primary stem is in all cases monostelic (pp. 102, 116) : it may con- 

 tinue to be monostelic (e.g. Lycopodiacese, Isoetes, Osniundacese, etc.), 

 but more commonly it becomes polystelic (most Filicinse). The 

 vascular tissue of the wood consists of lignified spiral (protoxylem) 

 and scalariform tracheides, or- less commonly vessels ; the bast 

 contains no companion-cells. The bundles are generally closed 

 and cauline. The relative arrangement of wood and bast in the 

 stele is generally concentric (see p. 124) in the Filicinse and 

 Selaginellacese, and radial in the Lycopodiacese : or the bundles 

 may be conjoint and collateral as in the Equisetinse and some 

 Filicinse. 



The reproductive organs are sporangia, generally borne on the 

 leaves (sporophytte) but sometimes directly on the stem (e.g. 

 Selaginella). Each sporophyll may bear many sporangia on its 

 inferior (dorsal) surface, as generally in the Filicinse and Equise- 

 tinse ; or a single sporangium on its upper surface (e.g. Lycopodium, 

 Isoetes), or in its axil (Selaginella). 



When the sporophyll bears many sporangia, they are usually 

 arranged in groups ; each group is termed a sorus, and the more 

 or less well-developed cushion of tissue from which the sporangia 

 spring is termed the placenta. The sorus may be naked ; or it 

 may have a membranous covering, the indusium (e.g. many 

 Filicinse). 



In the Filicinse the sporophylls are not confined to any special 



