FERNS. 



253 



which is fastened to the middle of the under side of this shield, 

 as seen in cross section in fig. 292. 



532. Sporangia. If we section through the leaf at one of the 

 fruit dots, or if we tease off some of the sporangia so that the 



stalks are still attached, and 

 examine them with the mi- 

 croscope, we can see the 

 form and structure of these 

 peculiar bodies. Different 

 views of a sporangium are 

 shown in fig. 293. The 

 slender portion is the stalk, 

 and the larger part is the 

 spore-case proper. We 

 should examine the structure 

 of this spore-case quite care- 

 fully, since it will help us to 

 understand better than we 

 otherwise could the remark- 

 able operations which it 

 performs in scattering the 

 spores. 



533. Structure of a spo- 

 rangium. If we examine 

 one of the sporangia in side 

 view as shown in fig. 293, 

 we note a prominent row of 

 1 the cells which extend around 

 the margin of the dorsal 

 edge from near the attachment of the stalk to the upper front 

 angle. The cells are prominent because of the thick inner 

 walls, and the thick radial walls which are perpendicular to the 

 inner walls. The walls on the back of this row and on its 

 sides are very thin and membranous. We should make this 

 out carefully, for the structure of these cells is especially adapt- 

 ed to a special function which they perform. This row of cells 



Rhizome with bases of leaves, and 

 Christmas fern. 



