64 



BOTANY AND PHARMACOGNOSY. 



starch and are used to some extent as foods, as Pteris esculenta of 

 China ; Pteridium aquilinum var. lanuginosa of the Canary Islands ; 

 Aspidiuni varium and Asplenmm bulbosum of Cochin China. 

 Polypodium vulgare contains a substance related to glycyrrhizin. 

 Adiantum pedatum and Polypodium Phymatodes are said to con- 

 tain coumarin, the latter plant being used in perfumery. 



Fig. 40. A water fern {Salvinia natans). A, a plant seen from side and showing 

 floating leaves at top attached to the horizontal stem, root-like finely divided leayes beneath, 

 and a cluster of globose sporocarps; B, a view from above showing especially the character 

 of the upper leaves; C, young plant developing from a megaspore (msp). — A, and B, after 

 BischofE; C, after Pringsheim. 



EQUISETALES. 



The Horsetails, or scouring rushes (Fig. 45, B) are peren- 

 nial plants containing a large amount of silicon in their tissues. Like 

 in the ferns the more or less branching, creeping rhizome persists 

 from year to year, sending out each year new shoots. As in some 

 of the ferns it develops two kinds of leaf-shoots, a fertile and a 

 sterile one (Fig. 45, B), each of which are distinctly jointed. 

 The scale-like leaves are arranged in circles about the joints or 

 nodes, the work of photosynthesis being carried on by the green 

 stems. The fertile branch develops at the apex a group of 

 sporophylls known as a cone or strobilus. The archesporium, or 

 initial spore-producing zone is unilocular. In Equisetum, the only 

 representative of the group, the spores are spherical and each is 



