320 PRACTICAL BOTANY 



II. Microscopic Investigation 



II. Cut transverse sections of the rhizome ofPilularia, 

 mount in glycerine, others in chlor-zinc-iodine, and 

 observe 



1. The epidermis, with a stratified outer wall, and 

 definite cuticle : stomata are to be found. 



2. The parenchymatous and starchy cortex, con- 

 taining large intercellular air-spaces, separated by 

 radiating diaphragms one layer of cells in thickness. 



3. The brown, well-defined endodermis, which 

 surrounds 



4. The cylindrical vascular bundle. 



5. Centrally may be seen a mass of sclerenchyma 

 surrounded and marked off from the bundle itself by 

 an inner endodermis. 



This is the type of structure for strongly grown rhizomes, but 

 where the rhizome is weak the inner endodermis and sclerenchyma 

 may be absent, and the vascular tissue then appears as a solid 

 strand. 



Examine the constituents of the bundle more care- 

 fully, and note a circular series of tracheides similar 

 to those in the xylem of other Ferns : this is surrounded 

 on either side by phloem, which is also similar to that of 

 other Ferns. 



Longitudinal sections of the same should also be 

 made, and the structure of the elements of the bundle 

 compared with that in homosporous Ferns. It is to be 

 noted that Pihdaria is a plant of aquatic habit, and 

 shows, in the presence of large intercellular cavities, 

 and in the reduced character of the vascular tissues, 



