154 



STRUCTURE AND LIFE HISTORIES 



performed by the foliage-leaves of other plants, the most 

 important of which are photosynthesis and transpiration. 

 143. Spore-bearing Leaves. The second type of fern- 

 leaf bears, on its underside, numerous "fruit-dots" or sori 



FIG. 113. Sporophylls of two ferns. At the left, a species of Poly podium 

 (Phymatodes) , having no indusium; at the right, Diplazium zdanicum. 



(singular sorus) (Figs. 112 and 113). These structures 

 have to do with reproduction. A single sorus of such a fern 

 as, for example, Polypodium irioides, is composed of a 



