CHAPTER VII 



SYNTHETIC TISSUE 



Under synthetic tissue are grouped all tissues and cells which 

 form substances or compounds other than protoplasm. Such 

 compounds are stored either in special cavities or in the cells 

 of the plant, as the glandular hairs; internal secreting cavities 

 of barks, stems, leaves, fruits, seeds, and flowers; photosyn- 

 thetic cells or cells with chlorophyll, and the parenchymatic 

 cells which form starch, sugar, fats, alkaloids, etc. 



PHOTOSYTTTHETIC TISSUE 



The most important non-glandular synthetic tissue is the 

 photosynthetic tissue, which is composed of the chlorophyll- 

 bearing cells of the plant. These are the so-called green cells 

 of leaves, of stems of herbs, of young woody stems, and in the 

 older woody stems of plants like wild cherry, birch, etc. The 

 greater part of the tissue of leaves is composed of chlorophyll- 

 bearing cells. 



Leaves collectively constitute the greatest synthetic manu- 

 facturing plant in the world, because the green cells of the leaf 

 produce most of the food of men and animals. The two com- 

 pounds utilized in the manufacture of food are carbon dioxide 

 (C0 2 ) and water (H 2 0). These two compounds are combined 

 by chlorophyll through the agency of light into starch. Chemi- 

 cally this reaction may be expressed as follows : 



6C0 2 + 5 H 2 = 2C 6 H 10 O 5 + 60 2 . 



During the day a large quantity of starch is formed. At 

 night through the action of a ferment the excess of starch remain- 

 ing in the leaf is converted into sugar (C 6 Hi 2 6 ) — C c H 10 O 5 + 

 H 2 = C 6 Hi 2 6 . In this form it is distributed to the living 

 cells of the plant. The presence or absence of starch in leaves 

 is easily ascertained by placing the leaf in hot alcohol to remove 



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