378 PART III. THE CLASSIFICATION OF PLANTS. 



In a few cases (e.g. species of Trichomanes and Lycopodium) 

 the gametophyte (prothallium) multiplies vegetatively by means 

 of gemmae, which are short spindle-shaped rows of cells in the 

 one case, and globular multicellular bodies in the other. 



The Life-History of the Pteridophyta presents in all cases, a 

 perfectly clear alternation of generations, the sporophyte and the 

 gametophyte being completely distinct. The oospore developes 

 into " the plant," be it Fern, Equisetum, or Lycopod, which bears 

 the sporangia and spores, and is the sporophyte. The spores, 

 when shed, germinate to form the gametophytes (prothallia) bear- 

 ing the sexual organs. 



In some cases among the Ferns, the transition from the one 

 generation to the other may be affected without the intervention 

 of a spore of any kind. Thus (e.g. Pteris crelica, Aspidium, falca- 

 tum, Todea africana), the sporophyte is developed from the game- 

 tophyte without the intervention of an oospore ; there are either 

 no archegonia on the prothallium (Pteris cretica), or if present 

 they are sterile ; the sporophyte is developed as a bud upon the 

 prothallium (apogamy, see p. 87). Again, in other species (Polij- 

 stichum angulare var. pulcherrimum, Athyrium Filix-fcemina var. 

 clarissima), the gametophyte is developed from the sporophyte 

 without the intervention of the asexually-produced spores (apo- 

 spory, see p. 87) : in the latter plant sporangia are developed, 

 but instead of producing spores they grow out into prothallia ; 

 in the former plant there is no trace of any sporangia, and the 

 prothallia are formed as outgrowths on the tips of the leaf- 

 pinnae. 



The Pteridophyta are classified as follows : 



Class V. FILICIN^E. The sporophyte is characterised by 

 having relatively large and few leaves ; the sporophylls are gener- 

 ally similar to the foliage-leaves and are not aggregated into 

 flowers ; the sporangia are numerous on the sporophyll (except 

 Isoetes) and are arranged in sori ; the archesporium is a single 

 cell (except Isoetes) ; the embryo has a primary root (except 

 Isoetes, Salvinia,'and possibly some species of Trichomanes) but 

 no suspensor. 



The characters of the gametophyte vary widely. The sper- 

 matozoids are multiciliate. 



Sub-Class HOMOSPORE^. The sporophyte produces spores of one 

 kind only ; the prothallia are, as a rule, monoecious, and become 

 free from the spore. 



