194 



PRACTICAL BOTANY. 



FIG. 119. A leaflet of Pteris aquilina, 

 showing the venation. (After Luers- 

 sen.) 



twenty-four hours ; wash out the carmine and stain with 

 methyl green for fifteen minutes. Wash out excess of 

 green in alcohol, clear in oil of cedar, and mount in Canada 



balsam as a permanent 

 preparation. 



5. Treat pieces of the 

 stipe with Schultze's 

 macerating mixture, 

 dissect, and find and 

 name as many tissues as 

 you can. 



6. Tear off a bit of the epidermis of the under side of 

 the leaf, taking care to secure some from over the veins 

 and some from between the veins. Sketch some of each 

 of the different kinds of cells you find, lettering the 

 sketch to show where each kind of cell is located. Notice 

 the stomata, each inclosed by two guard cells. The sto- 

 mata are the breath- 

 ing pores of the leaf. 

 Affected by variations 

 in moisture and light, 

 the guard cells change 

 their form and open 

 or close the entrance, 

 thus regulating the 

 admission of oxygen 

 and carbon dioxide to 

 some extent, and con- 

 trolling the evapora- 

 tion of the water ac- 

 cording to the neces- 

 sities of the plant. Do 

 you find nuclei in the guard cells? Do you find chloro- 

 phyl bodies in them? Do you find nuclei and chlorophyl 

 bodies in the epidermal cells ? 



FIG. 120. Cells from the under surface of 

 the leaf of Pteris aquilina, showing sto- 

 mata. (X480.) 



