PTERIDOPHYTA— LYCOPODIN^ 161 



The roots are adventitious as in other cases, even the primary 

 root proceeding from the epibasal half of the zygote. This pri- 

 BiSiYy root soon perishes ; the adventitious roots whicli succeed 

 it spring from the lower surface of the stem, or from peculiar 

 naked branches termed rhizophores, which grow down into the 

 soil and develop roots from their apices. 



The sporophjdls are usually aggregated at the ends of certain 

 of the branches ; they form their flowers nmch as in Lycopodium, 

 but there is not quite so sharp a distinction between the flowers 

 and the foliage leaves as in the latter case. The sporangia, which 

 are of two kinds, spring from the axils of the sporophylls, or 

 in some cases from the surface of the stem just above the inser- 

 tion of the latter. 



The macrosporangia usually contain four macrospores ; the 

 number of microspores is generall}^ large. 



In the details of its anatomy Selaginella presents some very 

 characteristic appearances. The apical meristem is sometimes 

 small-celled and stratified, but in some species there is a definite 

 apical cell. In others there is a group of two or three large cells 

 which behave like apical cells. The stem as seen in section 

 {fig. 919) is composed of parenchymatous or prosenchymatous 

 cells, embedded in which are one to three steles, the polystelic 

 condition being the most usual. There is no sclerenchyma, 

 and but few intercellular spaces ; sometimes, indeed, the latter 

 are absent altogether. Each stele is enclosed in a large air- 

 chamber, and this chamber is crossed by delicate rows of cells 

 or trabeculae, which attach the stele to the walls. The steles 

 are gamodesmic, and consist of a variable number of bundles 

 which have their protoxylem groups external, abutting on the 

 pericycle. A frequent number of bundles in the stele is two of 

 xylem and two of phloem ; in such case the structure much 

 resembles the stele of the fern stem, but it differs in the proto- 

 xylem being on the outside instead of being internal. The 

 structure is really of the same kind as in Lycopodium, the 

 bundles being originally disposed radially. Not bemg so nume- 

 rous as in the latter case, the subsequent fusions do not lead 

 to so complicated a woody mass. 



The leaves contain a single bundle, which in like manner is 

 slung in an air-chamber. The base of the leaf is sometimes 

 dilated into a kind of pulvinus, which is chiefly occupied by the 

 air-cavity. The intercellular space system being so much 

 reduced, the stomata of the leaf open into these air-chambers. 



The tissue of the root is more compact, there are no air- 



VOL. II. M 



