262 PHYLUM X. CALAMOPHYTA 



diameter. The epidermis is abundantly supplied with 

 stomata. 



466. The Wedge-leaved Calamites (Class SPHENO- 



PHYLLINEAE) were Paleozoic herbaceous 

 plants of moderate dimensions, whose sporo- 

 phyte stems were solid, jointed, grooved ex- 

 ternally, and at the joints bore spreading 

 whorls of wedge-shaped leaves. Their iso- 

 spores were borne in terminal cones com- 

 posed of whorls of 1- or 2-sporangiate spor- 

 ophylls. Sphenophyllum is the typical genus. 



467. In the Horsetails (Class EQUISETINEAE; of the 

 present, the plant-body of the sporophyte 

 consists of a hollow, elongated and jointed 

 herbaceous stem, bearing whorls of narrow, 



united leaves, which form close sheaths; the 

 stem is grooved, and is usually rough and 

 hard from the large amount of silica depos- 

 ited in the epidermis. 



468. The branches, when present, are in 



whorls. Both the main axis and the branches are in 

 most cases richly supplied with chlorophyll-bearing tis- 

 sue; but in some of the species the stems which bear 

 the spores are destitute of chlorophyll. All of the 

 species have underground stems, which bear roots and 

 rudimentary sheaths, and which each year send up the 

 vegetating and spore-bearing stems. 



469. The Horsetails are perennial plants. In some 

 species the underground portions, only, persist, the 

 aerial stems dying at the end of each year; these are called 

 the annual-stemmed species. In other species the 

 aerial stems persist; they are hence known as perennial- 

 stemmed. 



470. The epidermal cells are mostly narrow and 



