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 plastids) in which the chlorophyll is held. 

 These chlorophyll-bearing bodies, or chloroplast^ 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, 



