LITEEWOET 311 



the centre of each area look for a small circu- 

 lar opening, the stoma. Examine the under 

 surface of the thallus for root-like filaments, the 

 rhizoids. Are they abundant or few ? Do they 

 grow from any definite area of the under sur- 

 face ? Do they grow at the tips of the branches ? 

 "What is their average length ? Do they hold 

 the plant closely to the soil? What is their 

 color? Do they at all resemble the rhizoids seen 

 on Chara ? Look among the rhizoids for purple 

 leaves following the line of the midrib. Do 

 you find areolae and stomata on this sur- 

 face? 

 Make sketches of plants showing all of the features 

 studied. 



Microscopic St/ructure. 

 a. The tissues of the thallus. — Hold a piece of the 

 thallus of a living plant between two pieces of 

 pith, and with a sharp razor cut a series of thin, 

 transverse sections. Lay several of these on a 

 slide in a drop of water or fifty per cent, glycerine 

 and examine with the low power. If it is found 

 that the tissues of the living plant contain so 

 much air as to obscure the structure, use the sec- 

 tions of the fresh specimens only to get a general 

 idea of the structure, then work out the details 

 in alcoholic material. Notice the shape of the 

 section. How do you locate the midrib ? ISTotice 

 also that the section shows its upper surface to 

 be composed of a layer, the " epidermis," of clear 

 cells showing elevations (sections of stomata) here 

 and there. Below this layer comes another con- 

 sisting of dark-green cells, and this is succeeded 



