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A TEXTBOOK OF BOTANY [On. Ill, 4 



at will through the intercellular passages, and view the opera- 

 tions through the crystalline walls of the cells. Thus he 

 would see the water streaming in continuous current through 

 the ducts of the veins to the veinlets, and spreading thence 

 from cell to cell through walls and protoplasm until it satu- 

 rates every chlorophyll grain. Simultaneously the molecules 

 of carbon dioxide are moving in through the stomata and 



FIG. 11. Plan of the leaf as a photosynthetic mechanism. The chloro- 

 phyll grains (darkest shaded) are embedded in protoplasm (lighter shaded) ; 

 the water (horizontal lines) is brought by the duct (which lacks proto- 

 plasm but has a spirally-thickened wall) , and saturates every part of the leaf, 

 sap-cavities, and walls, except the outer walls of the epidermis ; the sugar 

 (crosses) and proteins (crossed circles) are removed in the protoplasm-lined 

 sheath and sieve cells ; the air-passages ramify to every cell, and open 

 through the stomata to the atmosphere. 



along the air passages, then through walls and protoplasm 

 to the same chloroplastids. On these green plastids falls a 

 flood of white sunlight, from which the chlorophyll stops the 

 effective red and blue rays, and turns their vibratory energy 

 against the assembled molecules of carbon dioxide and water, 

 which are thereby dissociated or shattered into their con- 

 stituent atoms, with an immediate recombination thereof 

 into grape sugar and free oxygen. The molecules of the 

 sugar, dissolved in the omnipresent water, diffuse from cell 

 to cell through protoplasm, walls, and sap to the nearest 



