96 A TEXT-BOOK OF BOTANY. 



rous, and the sporophyte produces two kinds of leaves, namely, 

 foliage leaves, and fertile leaves or those which bear the sporangia. 

 The sporangia occur on lateral branches of the sporophyll and 

 open at maturity by means of a horizontal slit. 



Ferns Used in Medicine and as Foods. Many of the ferns 

 contain tannin, a brownish coloring principle, and in addition 

 an anthelmintic principle. They may also contain ethereal oils, 

 starch, coumarin, aconitic acid, and other principles. A large 

 number have been used in medicine, of which the following may 

 be mentioned: Dryopteris (Aspidium or Nephrodium) maryinalis 

 and D. Filix-mas, yielding the official Aspidium. A number of 

 other species of Aspidium, as well as species of Adiantum, As- 

 plenium and Polypodium, are also used in various parts of the 

 world. The rhizomes of some of the ferns contain considerable 

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

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

 Aspidium varium and Asplenium bulbosum of Cochin China. 

 Polypodium vulgare contains a substance related to glycyrrhizin. 

 Adiantum pe datum and Polypodium Phymatodes are said to con- 

 tain coumarin, the latter plant being used in perfumery. 



EQUISETALES. 



The Horsetails, or scouring rushes (Equisetums), are peren- 

 nial plants containing a large amount of silica 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 distinct kinds of leaf-shoots, a 

 fertile and a sterile one, each of which is 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 representa- 

 tive of the group, the spores are spherical and each is furnished 

 with two spiral bands or elaters which assist in its dispersal. Some 

 of the Equisetums contain aconitic acid and are used in medi- 

 cine. Common scouring rush (Equisetum hyemale) is used for 



