THE BRACKEN FERN 



are themselves divided into smaller divisions, the lower ones 

 of which are again divided. The upper leaflets of the leaf 

 are less divided than the lower ones, and the uppermost 

 leaflets are very small and not divided at all. Several vascu- 

 lar btindles, branches of some of the bundles in the stem, 

 pass up the leaf -stalk into the central axis of the blade, from 

 which, in turn, bundles pass off into the midribs of the leaflets. 

 The bundles in each leaflet again separate and branch, and 

 their branches 

 divide still fur- 

 ther, so that 

 finally vascular 

 bundles pass 

 into all parts of 

 each division of 

 the leaf -blade. 

 These branching 

 bundles are the 

 veins of the leaf. 

 They look like 

 fine, light-green 

 lines when the 

 leaf is held be- 

 tween the eye 



and the light. On the under surface of the leaf are many 

 small air-pores (Fig. 52), which lead into spaces between the 

 cells in the interior of the leaf ; thus the inner cells can obtain 

 carbon dioxid from the air for the manufacture of carbo- 

 hydrates, as well as oxygen for respiration. 



129. Formation and Germination of Spores. — The spores 

 of the bracken fern are borne in small spore sacs, great 

 numbers of which grow in a line on the under surface of a 

 leaf and close to its outer edge. Not all the leaves, however, 

 bear spore sacs. The sacs are protected by the margin of 

 the leaf, which folds under so as to cover the sacs while they 



Fig. 52. — A, small part of a cross section through 

 a fern leaflet, showing spaces between the cells which 

 open to the outside through air-pores (a) in the 

 lower surface. B, an air-pore from the under 

 surface of the leaf ; it is a narrow opening between 

 two curved guard cells which are surrounded by- 

 larger cells of very irregular shape. 



