THE SCIENCE OF LIFE. 



to some of these plants being used as natural files for 



polishing various articles. 



The shoots are jointed, each articulation having a 



toothed membrane- 

 ous sheath, and hav- 

 ing whorls of branch- 

 es and branchlets. 

 The fructification is 

 in the form of termi- 

 nal cones, with scales 

 bearing spore-cases, 

 and opening by a 



FIG. 44. a. Equisetam arvense. o- Equisetum syl- 



vaticum. c. Section of the spike, d. A sporange. e. A longitudinal fisSUTC. 

 spore with its elaters coiled. 



Each of the spores 



has a pair of spiral filaments, with clubbed ends, and 

 attached by their center, so as to look like four stamens. 

 (Fig. 44.) 



4. FERNS in tropical countries are sometimes rivals of 

 the most beautiful Palms, having trunks varying from 

 two or three to sixty or eighty feet in height, formed of 

 the consolidated bases of the fronds. In these Tree- 

 ferns the fronds are either repeated in whorls, or they 

 form a tuft at the summit, constituting in the latter case 

 a collection of whorls with suppressed internodes. In 

 the ordinary ferns, or brakes, of temperate climes, the 

 stem is an underground one, or rhizome, and the dispo- 

 sition of the fronds is seldom observed. 



The epidermis of the stem is of a brownish hue, and 

 the general cellular structure, or parenchyma, consists of 

 many-sided nucleated cells, containing chlorophyll and 

 starch granules. There are also vessels (annular, spiral, 



