196 



PRACTICAL BOTANY, 



of the opposite side to break apart and scatter out the 

 spores. 



Imbed pieces of a fruiting frond between pieces of pith 

 and cut cross sections. Study the sporangia in situ in 

 these sections. Observe the position of the indusium. 



<st. 



ep. 



FIG. 122. Cross section of the midrib and adjacent parts of a leaflet of Pteris 

 aquilina. The fibrovascular bundle of the midrib is seen in the center, 

 supported above and below by prosenchyma, i.e., cells with greatly thick- 

 ened walls; i.s, intercellular spaces; st, stomata; ep, epidermis. (After 

 Sedgwick and Wilson.) 



Distinguish between the outer indusium formed by the 

 folding over of the edge of the leaf, and the inner or true 

 indusium formed by an extension of the epidermis of the 

 under side of the leaf. Draw. 



If fruiting fronds of Pteris are not easily obtainable, 

 substitute the sporangia of some other Fern ; for example, 

 one of the shield Ferns, 



