NATURE-STXTDY LESSONS. 103 



10. Draw a cross-section of the stem showing the 

 three distinct parts. 



1 1. Using a lens compare the cross-section of a stem, 

 one year old, with that of a stem several years old. 



12. Make longitudinal sections of parts of twigs of 

 various ages ; compare them and draw them. 



B. The Medullary Bays. 



13. («) Notice any radial markings to be seen in the 



longitudinal as well as in the cross-sections 



of the twigs. 



(b) Where are they found ? 



The bands of cellular tissue proceeding from the pith, or medulla, to the 

 surface are called medullary rays. 



14. Compare the wood in the medullary rays with that 

 about them. 



G. The Lenticels. 



15. {a) Observe the specks which are found in the 



bark of twigs. 



{b) How are they formed ? 



if) How are they arranged ? 



The loose mass of cells found in the bark are the lenticels. These per- 

 mit an interchange between the gases within the plant and the external air. 



D. The Bark. 



16. Make a cross-section of a twig of basswood. 



17. Compare this cross-section with that of the maple 

 twig. 



18. Examine the bark of the basswood twig to discover 

 its parts. 



19. Discover if the maple twig has the same parts in 

 its bark. 



