Ill KKDI1Y AM) EVOLUTION IN PLANTS 



that they are not all alike. Some of them are merely 

 foliage-leaves, and do not differ in any essential point from 

 the foliage-leaves of higher plants, such as the maple or 

 lily; they possess stomata for the exchange of gases and 



T'IG. 7. Portions of the sporophylls of two ferns to show the sori. 

 On the left Poly podi ion pimclalnm (L.) Sw.; on the ri^ht a variety of Pleris 

 longifolia, with sporangia marginal on (lie pinnules. 



water-vapor with the outer air (Fig. 5), and they also 

 resemble the leaves of higher plants in their internal struc- 

 ture. All fern-leaves, however, have a very characteristic 

 arrangement in the embryonic or bud condition, being 



