436 EQUISETUM LESS. 



Each axis rhizome and shoots terminates in a tetrahedral 

 apical cell. 



As in ferns, there is no primary root in the adult, but 

 numerous roots spring from the nodes of the rhizome, and 

 agree in all essential points of structure and development 

 with those of ferns. 



Some of the aerial shoots bear only leaf-sheaths and 

 branches, and are hence called sterile shoots: others, the 

 fertile shoots, terminate in a cone-like structure (Fig. 113, A), 

 formed of hexagonal scales (sp. ph\ at first closely applied 

 to one another at their edges, 'but afterwards becoming 

 separated. Each scale (Fig. 112, c, and Fig. 113, P., sp.ph) 

 is a mushroom-like body, springing from the axis of the cone 

 by a stalk (st) attached to the centre of the inner surface of 

 its expanded portion. Around the point of attachment of 

 the stalk spring from five to ten elongated sacs, the sporangia 



The structure and development of these mushroom-like 

 bodies or scales of the cone show them to be peculiarly 

 modified leaves, developed in whorls like the ordinary leaves 

 of the stem, but not cohering into sheaths, and assuming 

 the characteristic form just described in relation with their 

 special function of bearing the sporangia. We have there- 

 fore to distinguish, in Equisetum, between ordinary or 

 foliage-leaves and spore-bearing leaves or sporophylls. 



The spores are developed in the same way as in mosses 

 and ferns, but have a very distinctive structure. Outside 

 the usual double cell-wall is a third coat, which, as develop- 

 ment proceeds, becomes split up into four bands (Fig. 1 1 2, 

 D, E, /), wound spirally round the spore and attached to it 

 by one end, the opposite expanded end being free. These 

 bands or elaters are hygroscopic : when moist they are coiled 

 round the spore (D), when dry they straighten themselves 



