PTERIDOPHYTES 



97 



of the body is a spore-case, and all the spores are produced 

 in one continuous mass. In the independent sporophyte of 

 Pteridophytes, however, the root, stem, and leaves are the 

 conspicuous structures; and if the spores are to be formed 

 in the most exposed position it is evident that they should 

 appear in connection with the leaves. Therefore, among 

 Pteridophytes the spore-cases (sporangia) are produced by 



FIG. 77. Section through a sorus of a shield fern, showing the group of sporangia 

 covered by a shield-like (or umbrella-like) flap. After ENQLER and PRANTL. 



leaves, in some plants by all the leaves, in other plants only 

 by certain leaves. 



In the Club-mosses, with their small leaves, a single spo- 

 rangium is produced on the upper surfaco of the leaf near its 

 base (Fig. 75). In some of the Club-mosses every leaf has 

 a sporangium ; but in most of them only the uppermost 

 leaves have sporangia (Fig. 75). In the latter case, there 

 are two kinds of leaves on the plant ; (l) those that bear 

 sporangia, and (2) those that do not. The former are called 

 sporophylls (" spore-leaves ")> and the latter foliage leaves 

 (which means ordinary green leaves). 



