332 THE BIOLOGY OF THE PLANT 



Of those covering the veins ? Study the tri- 

 chomes. What is their shape ? Structure ? Do 

 they originate from particular cells ? How do 

 they compare with the root-hairs and with 

 those found on the rachis ? Look for stomata 

 surrounded by two kidney-shaped guard-cells. 

 Do you find them on both surfaces? Are 

 they abundant or few ? "What do the guard- 

 cells contain ? Do the epidermal cells have the 

 same contents ? Compare them with those seen 

 in Marchantia. 



Make drawings showing the arrangement of 

 the cells of the epidermis. Study transverse 

 and longitudinal sections of the pinnule. Does 

 it vary in thickness? ISTote the structure and 

 arrangement of the epidermal cells. Do they 

 contain chlorophyll ? How many layers in thick- 

 ness is the mesophyll ? Notice the arrangement 

 of the fibro-vasoular bundles. Draw a cross-sec- 

 tion as seen under the high power. Mount with- 

 out the drop of water and cover-glass a portion 

 of a pinnule bearing mature (brown) sori, and 

 with the low power examine its under surface. 

 Note the indusium covering dark-brown or 

 black bodies, .sporangia. What is the shape 

 of the indusium ? Color ? Does it entirely cover 

 the sporangia ? Does it bear trichomes ? Does 

 it differ in this respect from the epidermis? 

 With a dissecting-needle remove an indusium 

 to the slide and mount in a drop of fifty per cent, 

 alcohol. Expel the air, then examine under a 

 high power. What is the structure of the in- 

 dusium ? Do its cells resemble those of the 

 epidermis ? Does it have stomata ? In the same 



