RESPIRATION 269 



be free from vegetation. This treatment allows the water from 

 snows and rains to soak into the soil readily and also prevents 

 much loss of water through evaporation. This stored-up water 

 is then used by the crop during the second year. 



Many plants which live in dry regions have regions of water 

 storage. For example, the 

 Cacti store much water in 

 their stems and this storage 

 enables them to withstand 

 very dry periods. Some 

 plants, like the Begonia, have 

 special cells in their leaves 

 for the storage of water. 

 (Fig. 242.) In many plants, 

 as in Corn, much water is 

 stored in the pith. 



Thus it is seen that trans- 

 piration is helpful when the 

 water lost does not exceed ^- 242. -A small portion of across 



section ot a Begonia leaf, showing water 



the supply furnished from sto rage cells (a) and chlorenchyma (/). 

 the roots; also that the rate 



of transpiration depends much upon temperature, humidity of 

 the air, light, and velocity of the wind; and that the dangers of 

 transpiration may be overcome by modifying the transpiring 

 surface or by maintaining an adequate supply of water in the 

 soil or in storage regions of the plant. 



Respiration 



Although respiration is a fundamental process in all living 

 cells, leaves afford a good place for observing the outward signs 

 of it. Most of the oxygen used in the respiration of the plant 

 enters at the leaves from which place it is carried to all parts of 

 the plant. Also through the leaves much of the carbon dioxide 

 produced by respiration escapes to the air. Respiration and 

 photosynthesis, although occurring together in leaves, are wholly 

 separate processes as shown by the ways in which they differ. 

 First, photosynthesis occurs in chloroplasts and is a synthetic proc- 

 ess, in which the elements of carbon dioxide and water are built 

 into compounds with the storage of latent energy, while respira- 

 tion occurs in all parts of the protoplasms and is a process in which 



