A MANUAL OF BOTANY 145 



in the reference books. What part did the ancient horse- 

 tails have in the formation of coal ? What are the favorite 

 environments of phmts of this class ? Are they hydrophytes 

 (water })lants) or Xerophytes (dry land plants) ? 

 Drawings. Make the followini^ drawings: 



1. A complete horsetail (fertile and sterile stems and 

 rhizomes). 



2. Node of each (m) to show the scale leaves. 



3. Stem section (ni). 



4. Scouring rush, including strobilus. 



5. St^'obilus (m). 



6. Sporopliyll and spores (Ip). 



7. Stem (Ij}) to show section and stomates. 



Class 3. Club Mossp:s 



Habitat. Club mosses, such as lycopodium, are common 

 in northern evergreen woods. Selaginella is found native in 

 many suitable regions south of the evergreen belt. In all 

 large cities, however, a plentiful supply of selaginella may 

 be found, commonly in park greenhouses. Dried material 

 may be put up during the summer which freshens readily 

 when placed in water. The student will rarely see wild 

 plants, and so it is not a satisfactory field study. 



External features. Study selaginella and observe the posi- 

 tion of the plant in growth, its method of branching, and 

 the color and arrangement of the leaves. Observe also 

 the form, color, and place of origin of the aerial roots. 

 Examine the leaves (m) or (Ip) ; what are their forms and 

 exact arrangement on the stem ? Why are there two sizes 

 of leaves? Are stomates present or not? Study a cross 

 section of the stem and compare it with the section of a 

 fern stem, for any similar tissues. What purpose is ful- 

 filled by the air roots? 



Reproduction. Study a strobilus. How do the leaves 

 differ in form and arrangement from those of the stem? 



