58 



PLANT BIOLOGY 



ing an opening in the middle. This opening is 

 called a stoma, plural stomata (Greek, stoma = 

 mouth). Each stoma is surrounded by two 

 guard-cells. 



Make a diagram, greatly enlarged, of a stoma with its 

 guard-cells, together with the cells of the epi- 

 dermis that immediately surround it. Label 

 cells of the epidermis, guard-cells, stoma. 



upper epidermis 



chlorophyll bodies v ~ 



air space 



mesophyll cells con- 

 taining chloro- 

 phyll bodies 



lower epidermis 



stoma with a guard-cell on either side 

 FIG. 22. Cross section of a leaf. (Strasburger.) 



2. Study Fig. 22 and make out the shape and location of 

 each of the following parts of which it is com- 

 posed : upper epidermis, mesophyll cells, chloro- 

 phyll bodies, air spaces between the cells, lower 

 epidermis, stoma. In your note -book make a 

 drawing considerably enlarged showing a small 

 portion of the cross section, and label each part. 



68. Experiment to demonstrate the path of sap through 

 leaves. Laboratory Study No. 36. 



Place in red ink the lower end of a leafy branch of any 

 vigorous plant, e.g. geranium or bean seedling, and allow 



