32 A LABORATORY MANUAL OF BOTANY 
The stomata, having their openings passing through the 
epidermis and strengthening cells, and into the chlorophyll 
tissue. Where are the guard-cells? Are the stomata well 
protected? 
Surrounded by the green tissue is the central conduct- 
ing and pith region. Draw enough of the section to show 
the kinds of tissue and their arrangement. 
About what percentage of the leaf is doing chlorophyll 
work? Make a cross-section of a deciduous leaf, and com- 
pare in this respect. 
If leaves are to be retained during cold weather they 
must have special protection. What devices for protection 
_ do you see in this pine leaf? Has the size of the leaf any 
significance? The form? Could any other size or form be 
protected more easily ? 
Do you think the resinous substance has anything to do 
with the protection? What advantages have evergreen 
plants with reference to chlorophyll work? What disad- 
vantages? lvergreens are slow-growing plants. Why? 
Examine sections of the stems or branches of evergreen 
and of deciduous plants, and compare their protective 
structures. 
More than two years are required for the pines to ripen 
their seeds, consequently partially mature ones must pass 
through the winter. Examine young and old pine-cones, 
locate the developing seeds, and see how they are protected. 
LESSON XVII 
Autumn protection of deciduous plants 
Materials.—Plants with color beginning to change, some 
with leaves beginning to fall. The work is preferably done 
in the woods with trees and shrubs, such as oak, maple, 
hickory, elm, sumach, etc. 
