FOODS IN PLANTS 37 
35. Chlorophyll in the leaf. The so-called green cells of the 
leaf are not evenly green throughout, but contain special 
bodies (plasts, or plustids) in which the chlorophyll is held. 
These chlorophyll-bearing bodies, or chloroplasts, are often so 
numerous in the cells of the leaf as to make the cell appear to 
be almost of a solid green color, and when the surface of the 
leaf is observed, its appearance seems evenly green throughout. 
It must be clearly understood that chlorophyll and the 
chloroplast are not the same. Plastids (plasts) may or may 
not contain chlorophyll, just as a sponge may or may not con- 
tain water. A plastid can properly be called a chloroplast only 
when it contains chlorophyll. When green leaves have stood 
in alcohol for a few hours, the chlorophyll is dissolved by the 
alcohol, the leaf is decolored, and the color of chlorophyll may 
readily be observed in the alcohol. 
In summing up the structures of the leaf we may say that 
it usually consists of petiole and blade. The outer portions 
of the blade, both above and below, are the epidermis; in ad- 
dition to the ordinary epidermal cells the epidermis contains 
special structures, the stomata, each of which ordinarily con- 
sists of two guard cells and a stomatal cavity; within the 
epidermis are the veins and the masses of green tissue — the 
palisade and spongy tissues; within the cells of the green 
tissues, in addition to other cell contents, are many plastids. 
These may contain chlorophyll; they are then known as 
chloroplasts. 
36. Material for chlorophyll work. In the discussion of 
stomata it was stated that carbon dioxide may pass into the 
interior of the leaf. It was previously found that water is 
taken into the plant and carried through the stem. In the 
soil are many substances which are dissolved by the water, 
just as common salt or sugar would be. From this source 
there may pass into the plant compounds containing such 
things as nitrogen, potassium, phosphorus, sulphur, and iron. 
Carbon dioxide, which is secured through the surface of the 
leaf, is a gaseous substance which exists in the atmosphere, 
