132 REPRESENTATIVE PLANTS 



or flat ? Why do they grow in this manner ? How are they 

 attached to the earth ? What color and form have the thalli ? 

 Do they grow singly or in mats ? Take a specimen and 

 place it on the table. Observe the slowness or rapidity of 

 drying. 



External features. Place a well-formed thallus in a watch 

 glass. Examine for a midrib, wings, vegetative notches, 

 manner of branches, and hairs that attach it to the soil 

 (rhizoids). Examine the snrface for more or less regular 

 areas (stomata areas). What do you find in the center of each 

 area ? This is a stomate or mouth for the entrance and exit 

 of air and gases. 



Cupulas. On some thalli, observe the peculiar structure on 

 the upper surface appearing like tiny cups (cupules). Upon 

 what are they always situated ? If possible, find the different 

 stages from the young to the fully developed. How do they 

 differ ? Look inside of a f ul 1-grown one. What do you find ? 

 Examine the contained structure {cjemmce, buds) with (in) 

 and (/p), and observe the shape, color, and other features, and 

 in particular the notches and shining globules of oil near the 

 margin. Is the gemma a sphere or a flattened disk ? How 

 many are there in a cupule ? How many cupules are there 

 on a good-sized thallus ? These gemmae are reproductive 

 structures that are prepared for immediate growth and are 

 fine examples of vegetative multiplication. , Explain how a 

 gemma becomes a thallus, and how those from one thallus 

 may soon cover a considerable area with plants. 



Microscopic structure. Examine the lower surface for any 

 stomates (m). Are they present or not? Examine the 

 thin protective layer of cells which may be pulled off from 

 the upper surface of the thallus Qp). Study this epidermis 

 for the cells and the stomates. Observe the four guard 

 cells of the stomate. What is their use? What color, if 

 any, has the epidermis ? Examine, if possible, a section of 

 the thallus and observe, first, the upper and, second, the 



