REFERENCES 
365 
which might otherwise gain entrance to the interior of the 
tree and cause injury or death. 
SUMMARY 
The conifers belong to a class of the higher plants. They 
have periods of active and less active growth, both together 
resulting in the appearance of annual rings. Because their 
seeds are not entirely inclosed in an ovary, but lie uncovered 
on a scale, they are called gymnosperms. Conifers are of 
great economic importance, for they supply much of our 
lumber, tar, pitch, and all our turpentine and resin. Forests 
help to regulate the flow of streams and they prevent the 
washing away of the soil. 
QUESTIONS 
How are gymnosperms like other plants? How do they differ from 
other plants? What kind of trunk is characteristic of gymnosperms? 
How does a tree which grows in a forest differ from one which grows 
in an open field ? Why ? What are annual rings ? How are they 
formed ? Describe the branches; the leaves; the roots; the strobili; 
the fruit. What is a sporophyte? Name the gymnosperms. Make 
a list of the uses to which lumber is put. What other products come 
from the evergreen forests? In what ways are forests beneficial? 
What are the governments doing to protect them? What regions in 
your own state are covered with forests? 
REFERENCES 
Gymnosperms. 
Bergen and Caldwell, Practical Botany, pages 390-411. 
Coulter, Plant Life and Plant Uses, pages 195 and 196. 
Forestry. 
Government pamphlets and bulletins. 
Hough, American Woods. 
Keeler, Handbook of Trees. 
National Geographic Magazine. 
Sargent, Trees of North America. 
Schenck, Forest Policy. 
Snyder, General Science, pages 263-269. 
