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| Description: The saguaro also reduces its rate of evaporative water loss in several ways. First, like other cacti, it keeps its stomata closed during the day when transpiration losses would be highest. In the absence of transpiration, in full sun, the internal temperature of the saguaro rises to over 50°C, which is among the highest temperatures recorded in plants. However, as we noted for the camel, higher body temperature can be an advantage because it reduces the rate of additional heating. The saguaro's rate of heating is also reduced by the shape and orientation of its trunk and arms. At midday, when the potential for heating is greatest, the saguaro exposes mainly the tips of its arms and trunk to direct sunlight. However, the tips of the saguaro's arms and trunk are insulated by a layer of plant hairs and a thick tangle of spines, which reflect sunlight and shade the growing tips of the cactus.
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