THE BRACKEN FERN 



109 



135. Relatives of the Ferns : Water Fems. — With the 

 true ferns, of which about four thousand species are kno^ii, 

 and which include the brake and the others that have been 

 mentioned, are grouped about eight hundred other species 

 of plants whose relationship to 

 the fems is more or less close. 

 AH of these plants resemble true 

 fems in the fact that their asexual 

 generation is a large, highly de- 

 veloped plant, their sexual gen- 

 eration being small and incon- 

 spicuous. The Ti-'ater ferns are a 

 small group, living either on mud 

 or on the surface of bodies of 

 water. Their spore sacs are 

 formed inside a hard, nut-like 

 structure. The spores are of two 

 kinds : one kind, which is small, 

 develops into a small male plant 

 that bears antherozoids ; and the /'X ■ ^\'.: 



other kind, much larger, develops r~ ^ \r ■, 



fiG. 60. — Marsilea, one of 

 mto a female plant that produces the water fems. This plant 

 eggs. lives in verj- wet places, usually 



136. Horse-tails. — These, like on-mud the stem creeping along 



' the surface. Growing on the 



the brake, have an underground lower part of the left-hand leaf 

 stem. The stem sends up erect are two nut-like bodies. It is 



branches, whose appearance gives ^ ^^^^ '^"' "-^^ ^P°^^ °^ ^^ 

 ' '^'^ ° plant are borne. 



the plant its name. The lea^'es 



are very small scales which grow in circles upon the branch ; 

 the branch is green, and its cells manufacture most of the 

 plant's carbohydrate food. The upright branches have a 

 hard, rough surface, and some of the larger species are 

 called "scouring rushes," from the use to which they were 

 formerly put. The spore sacs are borne on leaves of a 

 special form which are crowded together at the upper end 



