194 ROUND THE YEAR 



frond while it is still very small and concealed within 

 the parent frond. Each of these rudiments becomes 

 enclosed in a special sheath formed by an overgrowth 

 of the frond upon which it is borne. The new fronds 

 are invariably paired at first, but one generally out- 

 strips the other, and. often only one comes to 

 maturity. The pointed end of every frond marks the 

 place where it was attached to its parent. Four or 

 five successive generations may be found still 

 fastened together, all of which are destined to break 

 away sooner or later. 



When a frond is studied microscopically, it is found 

 to be built up of small green cells. There is a faint 

 midrib and a pair of lateral veins. A considerable 

 part of the interior is occupied by air-spaces, which 

 are large in proportion to the cells and arranged in 

 one, two, or three layers according to the depth of the 

 frond ; it is these air-spaces which give to the frond 

 its remarkable buoyancy. The upper surface repels 

 water strongly when the plant is in good health ; the 

 lower surface is always wet. 



The flowers spring from clefts in the margins of the 

 fronds, and are enclosed by minute scales or bracts, 

 the outer one forming a sheath, which is burst at the 

 time of flowering. On one or both sides of the 

 flowering frond appears a group, enclosed by bracts 

 and consisting of a pistil and two stamens. The pistil 

 is flask-shaped, and surmounted by a hollow style, 

 open at the top ; each stamen bears two separate 

 anther-lobes, slightly divided into two cells. The 

 seeds ripen in autumn. They are minute (less than 

 I mm. long), oval and ribbed along their length. 



