82 STRUCTURAL BOTANY 



being borne on ordinary vegetative shoots, while in 

 others the aerial shoots branch little, or not at all. In 

 E. maximum, the largest British species, the barren stems 

 sometimes attain a height of six feet, but some of the 

 tropical kinds, such as E. giganteum, a native of tropical 

 America, are much taller, even, it is said, reaching 

 forty feet. 



B. EEPRODUCTIVE ORGANS 



The cone of an Equisetum is unlike the fructification 

 of any other living plant, and cannot be mistaken when 

 once seen, though the male flowers of some Coniferae, 

 such as the Yew, are found to bear a certain resemblance 

 to it when closely examined. The cone is terminal, 

 either on the main fertile shoot (as in E. arvense) or on 

 a branch (as in E. limosum). It consists of a fairly 

 stout axis, giving rise to densely crowded alternating 

 whorls of peltate scales (sporangiophores) on which the 

 sporangia are borne (see Fig. 38, 1, a). The scales of the 

 cone are usually called sporophylls, and their mode of 

 development agrees well with their leaf-nature, but some 

 of the fossil forms throw a certain amount of doubt on 

 this interpretation, so we prefer to call them simply 

 sporangium-bearers. In each whorl there are a consider- 

 able number of sporangiophores, about twenty in many 

 cases. Each sporangiophore has a short cylindrical stalk, 

 and expands at the end into a flat disc, to the under-side 

 of which the sporangia are attached, five to ten on each 

 scale. The peltate heads of the sporangiophores are in 

 such close contact that they usually become hexagonal 

 from mutual pressure. The sporangia extend inwards 

 as far as the axis, so as to fill up all the room that is 

 left between the peltate scales. They contain very 



