264 PHYLUM X. CALAMOPHYTA 



in height, but in certain tropical species attaining a 

 length of 10 meters or more. Among the better known 

 are the Common Horsetail {Equisetiim arvense), which 

 sends up short lived, pale or brownish cone-bearing stems 

 in spring, and profusely branching green stems in sum- 

 mer {E. telmateia, the Great Horsetail of Europe and our 

 own Northwestern region, resembles, but is larger than, 

 the Common Horsetail); the Woodland Horsetail {E. 

 sijlvaticum), whose green cone-bearing stems branch 

 profusely after fruiting, and persist all summer; and the 

 Scouring-rush, called also Dutch Rush {E. hiemale), 

 with green, branchless stems which produce cones, and 

 survive the winter. The genus Equisetum originated in 

 the Paleozoic period, and so is ver}^ old. Some of its 

 species have become extinct, as is the case with several 

 related genera. 



473. The Old Calamites (Class Calamarineae) were 

 Paleozoic plants whose sporophytes were 

 often trees, with hollow, jointed stems, 

 whose collateral vascular bundles allowed 

 an increase in diameter by the develop- 

 ment of a cambial zone. The leaves 

 were separate, narrow, and whorled at 

 op^'yte^anifspo^ea the joiuts of the stcm. The heterospores 

 of Old Caianute. ^^^^^ bome in terminal cones composed 

 of whorls of sporophylls, each bearing one or more spo- 

 rangia. Only fragmentary fossils of these plants are 

 known. 



Laboratory Studies, (a) Collect in early spring a number 

 of cone-bearing stems of the Common Horsetail. Note the 

 joints (nodes), bearing whorls of united flat leaves, and the 

 cone, composed of whorls of shield-shaped leaves (sporophylls). 

 Split the cone and stem and note that the latter is hollow, with 

 closed nodes. 



(6) Carefully dissect put a single sporophyll from the cone, 



