522 



BOTANY 



PART II 



The outer epidermal walls of the stem are more or less strongly impregnated 

 with silica. In Equisetum hiemale, and to a less degree in Equisetum arvense, the 

 silicification of the external walls is carried to such an extent that they are used 

 for scouring metal utensils and for polishing wood. 



Poisonous substances are formed in some species of Equisetum, and hay with 

 which the shoots are mixed is injurious to cattle. 



Order 2. Calamariaceae ( 132 ) 



This extinct order was highly developed in the palaeozoic period, especially 

 in the Carboniferous, when it was represented by numerous species. The plants 

 resembled the Horse-tails in general habit, but in some cases attained the size of 

 trees 30 metres high ; the hollow stem, which bore whorls of branches at the 

 nodes, was covered with a periderm, and underwent secondary thickening. 

 The leaves (Annularia, Fig. 488) stood in alternating whorls ; their form 

 was narrowly lanceolate and at their bases they united into a sheath. In the 

 most ancient type, Archaeocalamites (Fig. 488), they were dichotomously divided, 

 and thus more fern-like. The cones or flowers had in this genus the same structure 

 as those of Equisetum ; in most cases they were more complicated, whorls of 

 superposed scale-leaves separating the whorls of specialised sporangiophores. Each 

 of the latter was a stalked peltate disc bearing, on its under side, four sporangia 



(Fig. 489). In Calamostachys the 

 sporangiophores are placed some 

 distance above the corresponding 

 sporophylls, while in Palaeo- 

 stachya they stand in the axils of 

 the latter. They may be regarded 

 morphologically as special out- 

 growths of the scale-like sporo- 

 phylls. It is an interesting fact 

 that heterosporous as well as 

 homosporous forms occur among 

 the Calamarieae. 



CLASS III 

 Sphenophyllinae ( 132 ) 



This small class occupies an 

 intermediate position between the 

 Equisetineaeandthe Lycopodinae. 



The Sphenophyllinae were 

 represented by two genera in 

 palaeozoic times. Cheirostrobus 



from the Lower Carboniferous had 

 FIG. 490. 1, Sphcnophyttum, showing the branched stein i ,. . ., 



- with both Lear and wedge-shaped leaves and, on the COm f leX COlieS ofsimilar structure 

 right, an elongated cone. (After SCOTT.) 2, S. to those of the Galamarieae, but 

 emarginatum. (After SEWARD.) From LOTSY. approached Lepidodendron in 



anatomical structure. The species 



of Sphenophyllum which lived from the Devonian to the Permian periods were 

 herbaceous land-plants with elongated internodes. The stems, which underwent 



