LYCOPSIDA 57 



spirally, while the lateral branches are dorsiventral and 

 superficially frond-Hke. On these branches there are four 

 rows of leaves, two lateral rows of broad falcate leaves (Fig. 

 9M), an upper row of medium sized needle-hke leaves and a 

 row of minute hair-hke leaves along the under side. This 

 species, therefore, like several others in this section is highly 

 *heterophyllous'. The lateral branches in the more distal 

 regions of the plant are fertile and terminate in long narrow 

 strobih, which are frequently branched. As in the Clavata 

 subsection, the closely appressed sporophylls have, on their 

 dorsal (abaxial) side, either a bulge or a flange which pro- 

 vides some protection for the sporangia below. 



The apical region of the stem in Lycopodhim differs 

 markedly from species to species, for it is almost flat in 

 L. selago, yet extremely convex in L. complanatum. In the 

 past, opinions have diff'ered as to whether growth takes 

 place from an apical cell, but it now appears that this is not 

 the case^^ and that any semblance of an apical cell is an 

 illusion caused by studying an apex just at the critical 

 moment when one of the surface cells is undergoing an 

 obhque division. All species are now held to grow by means 

 of an 'apical meristem', i.e. a group of cells undergoing 

 periclinal and antichnal divisions. 



The sporehngs of all species are alike in their stelar 

 anatomy, for the xylem is in the form of a single rod with 

 radiating flanges. In transverse section these flanges appear 

 as radiating arms, commonly four in number. As the plant 

 grows, the later-formed axes of most species become more 

 complex, the xylem sphtting up into separate plates or into 

 irregular strands. However, some species retain a simple 

 stellate arrangement throughout their life, as in L. serration 

 (Fig. iiF) where there are commonly five or six radiating 

 arms of xylem. It is interesting that this species belongs to 

 the Selago subsection which on other grounds is regarded as 

 the most primitive, for some botanists, applying the doctrine 

 of recapitulation, have held that the embr>'onic structure of a 



