800 Lloyd, Tho Desert Botan. Laboratory of the Carnegie Instit. of Washington. 



hardly be regarded as regulatory of feranspiration in the sense of 

 certain previous students. 



This conclusion is strengthened by the results of experiments 

 on wilting, which in Verbena, show that, not only does an opening 

 of the stomata previous to wilting, as held by Leitgeb and Fr. 

 Darwin, fail to occur, but the closure aetually lags behind. Thns 

 the teleoligical significance of stomata on this score may very 

 seriously be called into question. 



Numerous experiments have shown that, under constant conditions 

 and in the total absence of light, the curve of transpiration shows 

 at about 6 A. M. a maximum which apparently must be interpreted 

 in terms of habit, that is as „eine von äußeren Einflüssen unab- 

 hängige Periodizität", thus giving support to Unger, Sachs and 

 Sorauer. This periodicity may not be interpreted as supposed 

 by Fr. Darwin and C. C. Curtis, to be dependent upon stomatnl 

 movements. 



The stomata of the plants studied are found to be devoid of 

 Chlorophyll, and this has been found true of a very considerable 

 numbcr of others. Contrary to the general supposition, these sto- 

 mata are quite as active, or indeed more so than in some instances, 

 as those possessing Chlorophyll. This fact, led the writer to 

 examine with great care the daily course of stomatal activity, with 

 respect not only to the movements, but also to the conditions of 

 the contents of the guard cells. It was found that the maximum 

 opening occurs in the summer at nine A. M. and continues tili 

 twelve M. The stomata then close slowly during one to three hours, 

 and remain almost closed tili sunrise on the following day. Further 

 light is thrown upon this procedure by the behavior of the con- 

 tents of the guard cells in Verbena, in which the amount of starch 

 is observably variable. The maximum starch content is to be found 

 during the night and tili sunrise. At this time the starch begins 

 to undergo depletion, until it is reduced to a minimum at from 

 nine tili 11. 30 A. M. aecording to the time of the year, the higher 

 temperatures hastening the depletion. Very soon the reverse takes 

 place, and the amount of starch again increases. This occurs in 

 the därk, and at both ends of the spectrum separately, and also in 

 the absence of Carbon dioxid. The Stimulus of light seems however 

 to be necessary to the opening of the stomata. We are thus able 

 to differentiate two distinet processes, mechanical and nutritive, 

 and to follow these separately. In addition to the starch content 

 there is present a certain times an oil 1 ) presenting, in some re- 

 gards an inverse action to that of the starch. It is present in 



1) Oil has of course been observed by various students in the guard cells of 

 stomata. 



