86 . PLANTS MAKE FOOD 



Conclusion. — 1. What seems to be one purpose of the veins? 



2. Remembering that the veins contain fibrovascular bundles, 

 the tubes which conduct fluids through the plant, determine 

 another function. 



3. How is the leaf fitted to receive light? Explain. 



Problem 68 : To study the microscopic structure of a leaf. 



Materials. — Leaf of geranium, glycerine, compound microscope, 

 glass slides, cover glasses, needles. Diagram, page 86, Civic 

 Biology. 



Method. — Remove with a needle a tiny portion of the under 

 surface of a leaf such as the geranium, or Tradescantia, mount in 

 water or glycerine, and examine with the low power of a compound 

 microscope. 



Observations. — Note numerous small structures (stomata) 

 scattered between the irregular cells of the epidermis. 



NOTE. — Each stoma is bounded by two bean-shaped cells, guard cells. By 

 slight changes of shape these control the size of the openings into the leaf. 



Study a cross section of a leaf cut through a stoma, or a good 

 chart showing a cross section through a stoma and a vein. Into 

 what do the stomata open ? The outer layer of cells, the epidermis, 

 has little chlorophyll. What function might these cells have? 

 (Look at the walls.) Beneath the epidermis find a layer of long 

 cylindrical cells, palisade cells. Do these contain chlorophyll 

 bodies? Below this layer note a layer of loosely joined cells, the 

 spongy parenchyma. Do these cells contain as much chlorophyll 

 as the palisade cells? How are they placed with reference to the 

 stomata? Look at the vein. Where would water pass through 

 it? 



Conclusion. — Knowing what you do about the use of a 

 green leaf to the plant, determine one use of the stomata. 



Drawings. — 1 . Cross section under microscope. Label all parts. 



2. Part of lower epidermis showing a stoma. 



Problem 69 : To show the effect of light on green leaves. 



Materials. — Oxalis or nasturtium plants. 



Method. — Place oxalis or nasturtium plants near a window. 



