172 



PRACTICAL BOTANY. 



supplementary guard cells and some of the surrounding 

 epidermal cells. Focus down and notice the number, 



shape, and arrange- 

 ment of the true 

 guard cells. Draw. 

 In a similar way 

 study the epidermis 

 of the lower surface 

 of the thallus. Draw 

 a few of the epider- 

 mal cells, selecting 

 some that show how 

 a hair originates. Do 

 you find stomata ? 

 Remove some of the 



FIG. 99 a. A portion of the epidermis of the 

 upper side of Marchantiapolymorpha, show- 

 ing areolse and stomata. (X 480.) 



hairs and study them under high power. Find two kinds, 

 the fine silky rhizoids, 

 situated directly under the 

 midrib, and coarser hairs, 

 showing projections extend- 

 ing inwards from a spiral 

 constriction. The outline 

 of the coarser hairs as seen 

 in optical section appears 

 scalloped. (Fig. 102.) 



Imbed a piece of the thal- 

 lus in pith and cut trans- 

 verse sections. Mount some 

 in water and some in alco- 

 hol. Draw an entire section 

 and indicate each of the 

 following parts on it. No- 

 tice the row of colorless 

 cells of the upper epidermis. Hunt along this row for a 

 section through a stoma. If one is found, draw it. Below 



Fio. 100. A vertical section through 

 a plant of Marchantia polymorpha, 

 showing a stoma at S, the air cav- 

 ity below it, and scales at EE. 



