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 De secaa eon 
special cells in their leaves EEA es 
for the storage of water. Raailsssewemiesbhe sa aera 
(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 . 
Fic. 242. — A small portion of a cross 
water lost does not exceed 3 : : 
E section of a Begonia leaf, showing water 
the supply furnished from storage cells (s) and chlorenchyma (f). 
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 
