34 REPRESENTATIVE PLANTS 



Structure. Examine the sections of the leaf (Jp) and 

 observe the epidermal layers and tlie green tnesophyll be- 

 tween. What color has the epidermis ? Are the cells thin 

 or thick? What purpose has this layer? What form 

 have the cells of the mesophyll ? Are they alike in shape 

 throughout, or are some elongated perpendicularly to the 

 epidermis (^palisade cells) ? If the section shows them, 

 examine the stomates, and determine what they open into. 

 If a vein is cut across, study its cell structure and compare 

 it with the vascular bundles in ferns or in stems of seed 

 plants. Notice the hairs and discover to what part of the 

 leaf they are attached. Draw the leaf section and any 

 details of cell structure observed. 



Description. Write a careful, complete description of the 

 geranium leaf, answering all the questions. Read about 

 " Geranium " and " Pelargonium " in a good encyclopedia, 

 and learn the peculiar features of these plants, and decide 

 which name really belongs to your plant. 



2. Venatio]^ and Vernation 



Statement. A great variety of leaves may be used and 

 ought to be compared by the student with the types given in 

 these exercises. For convenience, the venation study is 

 based on the following leaves, all easily obtainable : grass 

 leaves, Wandering Jeiv (Tradescantia), hyacinth, evening 

 primrose, elm, oak, maple, violet, ivy, begonia, pine, spruce. 



Forms of venation. The pinnately veined and palmately 

 veined leaves have been defined in the geranium study. 

 Two other forms of venation may be recognized: parallel- 

 veined, viz., when the main veins run from the base to the 

 apex and are more or less parallel, and finally the peculiar 

 needle leaves of the spruce and pines, with generally one or 

 two central veins. Examine any of the above-named leaves 

 or any others furnished and determine the method, of vena- 



