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 mi<>roscopic 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 imder 

 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 niimerous 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 Httle 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. 



