4 io TEXTBOOK OF BOTANY 



6. Study a cross section through a part of a branch that is three 

 or more years old. Compare it with the section previously studied. 

 What changes have taken place in the wood ? In the bast ? Where 

 are the new cells being formed which add to the thickness of the 

 branch? What kinds of cells do you find in the medullary rays? 

 Can you distinguish between spring and summer wood ? Why can 

 we tell the approximate age of a tree or of a branch by counting 

 the annual rings? Is bark being formed? If so, can you make 

 out in the section how its formation goes on? In what parts of 

 the stem do you find resin passages? Draw a portion of this 

 section. 



6. Where and how are the small staminate cones of the pine 

 borne ? What are the parts of a cone ? 



7. Examine a single microspore leaf torn from a staminate cone. 

 Do you find pollen sacs ? How many ? Where are they borne ? 

 Draw a microspore leaf showing the pollen sacs. 



8. Break open a pollen sac and examine with a compound 

 microscope the pollen grains that escape. Draw a single pollen 

 grain. 



9. Compare a young carpellate cone with a staminate cone. Is 

 it made up of similar parts ? How are the carpellate cones borne-? 

 On what part of a branch do you find the youngest cones? The 

 year -old cones ? The ripe cones ? 



10. On what part of a macrospore leaf are the macrospore sacs 

 (ovules) borne? How many macrospore sacs on a leaf? What 

 parts can you make out in 'a sac? Draw a macrospore leaf, show- 

 ing the sacs. 



11. Compare a year-old cone with the young cone just studied. 

 What changes have taken place in the macrospore leaves ? In the 

 macrospore sacs ? 



12. Study a still older cone, bearing mature seeds. From what 

 has each seed developed ? What is the wing-like structure attached 

 to a seed ? How do the seeds escape from the cone ? 



13. "Nut pine" seeds are best for the study of the structure of 

 the seed. On the outside is a hard coat ; from what did it develop ? 

 Crack open this coat ; is there an inner seed coat ? Inside find the 

 endosperm and the embryo. Of what parts is the embryo com- 



