PTERIS AQUILINA. Ill 



b. Here and there narrow slit-like stomata, each consisting 

 of an opening bounded by two crescentic cells, the 

 guard-cells. 



c. Along certain lines (over the veins) the different shape 

 of the epidermal cells. 



d. The chloroplasts, especially in the guard-cells. 



e. Make a drawing showing these points. 



/. Examine in the same way the epidermis of the upper 



surface of a leaflet; note the absence of stomata. 

 2. Make a transverse section of a leaflet, 1 mount, and observe: 



a. The upper and lower epidermis; the sections of stomata 

 appearing in the latter. Note also the substomatal 

 chamber within the green tissue. 



b. The mesophyll, the chlorophyll-bearing tissue. 



c. The veins. 



d. Draw. 



IV. SPORANGIA AND SPORES. 



From a ripe sorus remove and mount some sporangia. In 

 a perfect specimen observe: 



1. The stalk on which it was borne. 



2. The form of the main body or spore-case. 



a. On one edge note the row of heavy-walled cells, the 

 annulus. Where are its ends? 



b. The cells that form the rest of the wall. 



3. The spores. 



4. Draw. 



5. Place on the slide some sporangia that have been moistened 

 in water, allow them to become dry as they are observed 

 with the low power, and determine just how the sporan- 

 gium acts in expelling spores. Make diagrams illustra- 

 ting the changes in position of the annulus and the side 

 walls during this process. 



1 These leaf sections will be most satisfactory if made from material 

 imbedded in paraffin. 



