FILICES. 543 



branches having a straight vernation occupying their place. The 

 cuticle exhibits a longitudinal series of stomata. A spiral structure is 

 observed in some of the vessels. Eeproductive organs collected into 

 cones; spore-cases (theca? or sporangia) attached to the lower surface 

 of peltate polygonal scales (fig. 766), and opening by an internal 

 longitudinal fissure (fig. 767); spores in the form of rounded cells, 

 surrounded by 2 elastic, club-shaped, hygrometric filaments or elaters 

 (figs. 768, 769). Plants with simple or branched stems, the branches 



768 769 



being jointed and placed in whorls at the articulations of the stem, each 

 whorl consisting of as many branches as there are teeth in the sheath. 

 Found in ditches, lakes, and rivers, in various parts of the world. In 

 South America, Gardner measured an Equisetum fifteen feet high, and 

 three inches in circumference at the lower part of the stem. There is 

 only 1 known genus, comprehending about 12 species. Example 

 Equisetum. 



1107. From the quantity of silicic acid contained in them, some of 

 the species of Equisetum are used in polishing mahogany. An analysis 

 of them is given at ^[ 226. The spiral filaments which surround 

 their spores are interesting objects under the microscope, exhibiting 

 marked movements according to the moisture or dryness of the atmo- 

 sphere around them. The stomata are arranged in lines on the 

 cuticle. In Equisetum hyemale, often called Dutch Eushes, the sili- 

 ceous stomatic apparatus is well seen after the action of nitric acid on 

 the stem. There are regular rows of tubercles of a siliceous nature, in 

 each of which is a transverse fissure, and at the bottom of the fissure 

 a stoma is placed, with its opening at right angles to that of the 

 tubercle. Each portion of the stoma has a pectinated (comb-like) 

 appearance. The distinctions between the species of Equisetum are 

 founded on the nature of the fertile and barren stems, the number of 

 stria3 or furrows, and the number of teeth at the articulations. 



1108. Order 213. Filices, the Fern Family. Stem, a rhizome 



Figs. 766-769. Reproductive organs of Eqniseturn, to illustrate the natural order Equisetaceje. 



Fig. 766. A peltate or polygonal scale, e, taken from the terminal cone-like fructification of an 

 Equisetum. c, Thecse or spore-cases arranged in a verticil on the under surface of the scale. 

 ;>, Stalk by which the scale is attached to the axis. 



Fig. 767. <, Spore-case seen on its inner surface, with the slit or opening by which the spores 

 are discharged. 



Fig. 768. A spore, s, with the two clavate filaments rolled up in a spiral manner around it. 



Fig. 769. Spore, , with the two filaments, which are clavate at each extremity, unrolled. 

 These filaments or elateis are hygrometric, and move about under the influence of moisture. 



