NATUBE-STUDT LESSONS. 133 



(c) Can you find any part where the stem is solid ? 

 '^d) What marks the outside of the stem in such 

 places ? 



12. Trace the connection between the leaves and the 

 solid zones of the stem. 



1 3. Compare the leaf of the maple or willow or plan- 

 tain with that of the oat. 



14. («) To what part of the other leaf does the sheath 



of the oat-leaf correspond ? 

 (^) How are the leaves of the oat arranged on the 

 stem? 



(c) Compare this arrangement with that of the 



leaves in the maple. 



(d) How does the sheath of a grass-leaf like the 



oat differ from that of a sedge-leaf.' 



15. What advantage to the oat or Indian-corn or 

 timothy or other grass plant is it to have its petiole (that 

 is its leaf-stem) in the form of a sheath ? 



16. («) Observe the thin guard (the ligule) at the top 



of the sheath of the grass-leaf. 

 {b) Discover its use. 



17. When an oat plant is bent or trodden down, where 

 does it bend to straighten itself? (Perhaps the advanced 

 pupils can discover how it accomplishes this bending at 

 the joints or nodes!) 



18. Observe how the oat-leaves in the field crop are 

 adapted to securing the necessary amount of light and 

 heat 



19. Why are windy situations favorable to grass crops, 

 particularly those that bear grain, like wheat, barley and 

 corn? 



