BOTANY — LIVINGSTON, LLOYD. I 29 



(10) The effect of air currents in increasing evaporation and trans 

 piration rates is so great that reliable measurements of transpiration 

 can not be made in closed chambers. 



(11) By a new method, involving a newly devised evaporimeter, a 

 physiological regulation of the rate of transpiration was unquestion- 

 ably shown to exist in the forms studied. 



(12) The regulation of transpiration seems to be controlled by air 

 temperature, the checking of water loss beginning to be effective 

 between 79 and 90 F., and the check being removed between 75 

 and 8o° F. 



(13) The ratio of transpiration rate per unit leaf surface to evap- 

 oration rate per unit water surface is termed relative transpiration. 

 Relative transpiration is reduced by the regulatory response from 

 unity in the high periods to from one-twelfth to one-sixth in the low 

 periods. 



Lloyd, Francis E., Columbia University, New York, N. Y. Grant 

 No. 285. Study of correlation between stomatal action and trans- 

 piration in types of desert pla?its. $500- 



Abstract of Report. — The results of the previous summer's work 

 upon Fouquieria sp/endens were reexamined and verified. The work 

 this summer (1905) was based more particularly upon Verbena ciliata. 

 All the investigations have been carried on at the Desert Botanical 

 Laboratory at Tucson. 



The conclusions reached are as follows: 



The direct observation of stomata at all hours of the day and night 

 indicates that the normal changes which occur in the form of the 

 stomata are slow. Rapid changes do not appear to occur except dur- 

 ing rapid wilting. The quantitative study of this phenomenon and 

 the observation of stomata in controls have resulted in the conclusion 

 that the closure not only does not occur in anticipation of ' ' visible 

 wilting" (of certain authors), but, quite contrariwise, lags behind. 

 The view that the stomata are devices with large efficiency to control 

 transpiration is thus called into question. Although the rates of 

 transpiration during the day and night have not yet been fully worked 

 out, it is probable that the curve expressing them will be similar 

 to that constructed for Fouquieria splcyidens. This probability is 

 increased by the fact that the maximum opening of the stomata is 

 between 8 and 9 a. m. (in the summer months), several hours before 

 the maximum rate of total transpiration, according to the usual 

 expectation, is reached. 



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