CHAPTER XXIV 

 THE LOSS OF WATER VAPOR FROM PLANTS: TRANSPIRATION 



Transpiration is essentially the evaporation of water from within plants. 

 It includes both the vaporization of water at all cell surfaces exposed to 

 the air and the subsequent diffusion of the vapor into the atmosphere 

 surrounding the plant. In the chapters immediately preceding it was 

 apparent that the diffusion of water molecules is a primary process in 

 imbibition and osmosis. It is also a primarv process in transpiration. 



Transpiration is the most generally recognized of all processes in 

 plants. Among the common practices based on this recognition are the 

 daily watering of house plants; the elaborate systems of overhead and 

 underground irrigation of gardens; the wrapping of cut flowers and 

 freshly dug plants in waxed paper or other waterproof containers; the 

 packing of nursery stock in moist sphagnum moss for long shipments; 

 the enclosing of fruit and vegetables in oiled clotli or covered dishes in 

 electric refrigerators; the periodic sprinkling of the floor and crates in 

 the low-temperature storage of apples; and the placing of glass or paper 

 covers over newly transplanted seedlings in the garden. These and 

 many other practices are attempts to reduce the more harmful effects of 

 evaporation of water from plants or isolated parts of plants. 



Transpiration not limited to leaves. Transpiration mav occur from the 

 surface of any plant organ. E\en the bark of trees does not prevent it 

 entirely. "Sun-scald" of trees that have been transplanted from nurseries 

 where their stems were shaded is the result of heating and drving bv 

 direct sunlight. Mature potato tubers, in spite of a cork covering, lose 

 noticeable amounts of water and shrivel in the course of time. The 

 evaporation of water from roots in dry soil, or from roots during the 

 process of transplanting may result in serious injury or death. Transpira- 

 tion from fruits in drought periods may result in shrinkage. The tips of 

 tomato fruits mav die as a result of excessive transpiration. The subse- 

 quent decay of these dead portions of the fruit is referred to as "blossom- 

 end rot." After removal from the plant such fruits as prunes and grapes 

 are often artificially exposed to warm dry air to hasten the loss of water 



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