Biology of Higher Plants — Anatomy and Physiology 237 



amount of carbohydrate produced depends on their joint action. What 

 may be a limiting factor in one plant under certain conditions may not 

 be a limiting factor in another plant under different conditions. 



The anatomic construction of the leaves and their stomata influence 

 photosynthesis. Foreign materials, dirt, and rain in the stomata inhibit 

 the exchange of gases, and hence influence photosynthesis. The pre- 

 dominance of stomata on the underside of leaves makes this a factor 

 of less importance than if the stomata were on the upper surface. 



7. Atmospheric Pressure: Variations in atmospheric pressure de- 

 cidely influence photosynthesis; when the pressure is high, the rate is 

 increased. 



Applied and Commercial Aspects of Photosynthesis. — In most plants 

 the demonstrable products of photosynthesis are sugars and starch. 

 Starch is an ideal storage product because it cannot pass through the 

 cell walls due to its insolubility. Some plants, such as the onion/ pro- 

 duce no starch, while others produce an oil instead of starch. The 

 carbohydrates formed by photosynthesis are the building stones of which 

 the plant builds proteins, fats, oils, etc., as shown by the following: 



Carbohydrates + Nitrogen -> Amino acids (each -> Proteins 



(glucose, cane Phosphorus molecule has the 



sugar, starch) Sulfur amino or NH2 group) 



Carbohydrates (by fermentation) -> Glycerin \ p . 

 Carbohydrates (by oxidation) -^ Fatty acids T' 



Most of the radiant energy absorbed by green leaves is transformed 

 into heat energy which through radiation raises the temperature of the 

 surrounding air. In this manner some of the heat energy of the sun 

 is captured and radiated for use by other living organisms. Some of 

 this heat energy also vaporizes the water within the leaf. Some of the 

 light energy absorbed by chlorophyll rpay be transformed into electric 

 energy, which may explain some of the electric phenomena of living 

 plants. 



The close chemical relationship between chlorophyll A and the blood 

 pigment (hematin) has caused much scientific investigation. When 

 chlorophyll is decomposed by acids or alkalies, the residue (hemopyrrole) 

 has a chemical composition similar to that of hematin which is derived 

 from the decomposition of red blood pigment. In hemopyrrole the 

 metallic element involved is magnesium; in hematin it is iron. 



Chlorophyll has long been considered to be of dietary value to ani- 

 mals although its exact significance has not been determined. More 



