34 



A TEXTBOOK OF BOTANY 



[Ch. hi, 4 



at mil 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 ceh 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 

 phyll grains (darkest shaded) 

 the water (horizontal lines) 

 plasm Imt has a spirally-thick^ 

 sap-cavities, and walls, excc[: 

 (crosses) and proteins (crosse' 

 sheatli and sieve cells : the 

 through the .stomata to the 



as a photosjnthetic mechanism. The chloro 



are embedded in protoplasm (lighter shaded) ; 

 is brought by the duct (which lacks proto- 

 ened wall) , and saturates every part of the leaf, 

 t the outer walls of the epidermis : the sugar 

 d circles) are removed in the protoplasm-lined 



air-passages ramify to every cell, and open 



atmosphere. 



along the air passages, then through walls and protoplasm 

 to the same ehloroplastids. t)n these green plastids falls a 

 flood of white sunlight, from which the chlorophyll "^tops the 

 effective red and blue rays, and turns their vibratory energy 

 against the assembled molecules of carlion dioxide and water, 

 which are thereby dissociated or shattered into their con- 

 stituent atoms, with an immediate recomliination 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 



