Cannon : Transpiration of Fououieria 



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droughts apparently the most extreme, and it flourishes in habitats 



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which are so dry as to be unfit for many desert plants. 



A characteristic specimen of ocotillo is composed of a num- 

 ber (a dozen or more) of fairly straight branches, for the most 

 part simple, which arise from the short main stem near the ground 

 (figure 4). The branches are from 2 to 5 meters in length, and 

 bear spines which are regularly placed and which are morpholog- 

 ically midribs of the primary leaves. 



During the dry seasons the branches are naked, but in the 



Figure 4. Foiiqnieria splendent in leaf. 



rainy ones they are well covered with rosettes of small leaves 

 which are borne in the axils of the spines. The variation in the 

 foliage is not a seasonal phenomenon but is directlyassociated 

 with the distribution of the rainfall. Although seemingly lifeless 

 during the droughts the plant is not dormant, since beneath its 

 gray exterior there is chlorophyl-bearing tissue which enables the 

 photosynthetic processes to go on, even if in a feeble manner, and 

 consequently some transpiration may always be detected. When 

 the rains return new leaves are formed with a promptness that is 



