144 REPRESENTATIVE PLANTS 



do you ti lid? In particular, observe the rows of stomates, 

 or ])ores. Rub the sterile stems between your fingers, and 

 also on apiece of rusty tin. What do you notice? Examine 

 (m) sections of the sterile and fertile stems. What do you 

 find ? Explain any advantage of this condition to the plant. 

 Examine the underground stem (rhizome) and find whether 

 each kind of aerial stems is connected to it. How do the 

 appearance, markings, and parts correspond to those of the 

 aerial stems? Where are the roots attached? Are there 

 any evidences of buds ? 



Scouring rush. Examine now a scouring rush. What 

 structure takes the place of the aerial stems of the horse- 

 tail ? Observe on this stem the different features found in 

 the horsetail. There may or may not be branches. What, 

 in particular, are the number and arrangement of the sto- 

 mates {vl})) ? Determine in the same manner as for horse- 

 tails the roughness of the stem. What do you fiud? Is 

 the name appropriate? 



Reproduction. Examine fruiting cones {strobilus) of the 

 horsetail, or preferably those of the scouring rush. Where 

 are they situated? What is their general appearance? 

 Observe the platelike structures that make up the outer, 

 surface (sporophylls); What is the form of each plate? 

 Examine (m) a single detached sporophyll, side view, with 

 its stalk and expanded end. Study the saclike structures 

 (sporangia) surrounding the stalk, and attached to the inner 

 face of the plate. How many are there, and how do they 

 correspond to the number of sides in the plate ? Crash a 

 sporangium and observe the spores (Ijj). What is their color 

 and shape ? What is attached to them ? These structures 

 are called elaters. 



Breathe on some spores, very gently, and observe the 

 results (Ip). What x^urpose may be attained by this 

 peculiar action ? What use was made of scouring rushes 

 in olden times ? Read about " Calamites " and *' Silica ^' 



