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 Folypodium 
(Phymalodes), having no indusium; at the right, Diplazium zelanicum. 
(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 
