A Synopsis of Plant Phyla 45 



with creeping steins which bear fiHform or long petioles and 

 4-parted leaves. Marsilia, Pihilaria. (Pf. I, 4, 403.) 



Family 13. Salviniaceae. Very small, floating, annual plants, 

 with horizontal stems which bear minute distichous leaves. 

 Acolla, Salvinia. (Pf. I, 4, 383.) 



Phylum X. CALAMOPHYTA. The Horsetails. 



Chlorophyll-green, terrestrial plants, exhibiting two genera- 

 tions in each life cycle, viz., (i) the gametophyte, which is small, 

 and short-lived, and (2) the sporophyte, which is large, with 

 roots, stems, and leaves, and long-lived. Stems of the sporophyte 

 solid or hollow, jointed, erect or creeping; leaves whorled, rela- 

 tively small. This phylum has almost become extinct, being rep- 

 resented today by but a single genus of 24 species. 



Class 22. SPHENOPHYLLINEAE. Palaeozoic plants of 

 tree-like aspect and dimensions, long since extinct. Stems solid, 

 jointed, with a central triarch, fibrovascular bundle, and bearing 

 relatively small, wedge-shaped leaves. Sporophylls in cones, each 

 sporophyll with one or two isosporous sporangia. 



Order Sphenophyllales. With the characters of the class. 



Family i. Sphenophyllaceae. Known only from fossil speci- 

 mens. Sphenophyllum. (Pf. I, 4, 515.) 



Class 23. EQUISETINEAE. Palaeozoic to recent plants, 

 mostly extinct. Stems hollow, jointed, with a circular row of 

 collateral fibro-vascular bundles ; leaves very small, narrow, and 

 united into a sheath (in recent forms, larger in Mesozoic forms). 

 Sporophylls peltate, in close terminal cones, each sporophyll with 

 several pendent, isosporous sporangia. 



Order Equisetales. With the characters of the class. 



Family 2. Equisetaceae. Including but one living genus, 

 Eqitisctutn, which has survived from the Carboniferous period, 

 and several extinct genera, Plqiiisctitcs, Phyllothcca, and others. 

 (Pf. I, 4, 520.) 



Class 24. CALAMARINEAE. Palaeozoic plants, often of 

 tree-like aspect and dimensions, long since extinct. Stems hol- 

 low, jointed with a circular row of collateral fibrovascular bun- 



319 



