Cannon: Transpiration of Fououieria 413 



Summary and conclusions 



The leading points in this paper together with the conclusions 

 may be briefly stated as follows : 



\ 



1. The noteworthy feature of the climate of 1904 was the 

 small precipitation, which was 75 per cent, normal. The rainfall 

 was so distributed that little of it occurred in winter, spring or 

 early summer, most of it coming in midsummer. Thus during 

 most of the year the conditions of plant life were very severe ; 

 but in August especially they were favorable to plant growth, 



2. The customary fleering vegetarion of late winter and of 

 spring, composed mainly of annuals, did not appear, and tlie larger 

 and long-lived forms either did not put on leaves at the time at 

 all, or if they did so they were dropped when droughts returned. 

 In summer, however, ail vegetation was very luxuriant 



3. Although without leaves during periods of drouth Fouqidcria 

 nevertheless maintains at such times a feeble rate of transpiration. 



4. Air-dry stems o{ Fouqidcria in place can absorb hygroscopic 

 moisture in appreciable amounts. 



5. The rate of transpiration o{ Fouqnieria^ and of other shrubs, 

 varied directly with the water-supply. The rate increased as an 

 immediate effect of the rains and it decreased as the time past the 

 rains became greater. Accompanying the increase in rate there 

 was always an increase in the transpiring surface (although the 

 rate may increase without the latter), but a decrease in the rate 

 occurred without an immediate and corresponding decrease in the 

 transpiring surface, although in the end this always became less. 



6. The least rate of transpiration, when leaves were present, 

 u^as observed during the dry and cool period the latter part o^ 

 March. At this time a rate of .22 milligram per minute for 100 

 sq. cm. of leaf surface was recorded. The highest rate waa 

 observed August 26, near the close of the summer rains when the- 

 temperature was hi£^h. The Auerust rate for the same time andl 

 area as in March was 8.25 milligrams. 



7- A very striking adaptation to desert conditions is to be 

 found in the promptness with which Fouquieria forms leaves whem 

 the water-supply of the plant is increased by the rains. ' As an 

 example of this the following instances may be presented : For 

 several weeks previous to the nth of May one of the plants 



