Lloyd, The Dcsert Botan. Laboratory of the Oarnegie Instit, of Washington. 799 



from unity in the high periods to from l /i2 'o l / lö in Iho low 

 periods. 



Professor V. M. S palding began Ins work at the Desert La- 

 boratory in the autumn of 19015, having reeeived leave of absence 

 from the University of Michigan fOr this purpose. He undertook 

 an investigation of the biologieal relations of certain desert slirubs 

 which exhibit a wide ränge of adaptibility, retaining inore or less 

 pionounced mesophytic habits, but capable of surviving extreme 

 drouth and usually classed as typical xerophytes. The success of 

 these plants in resisting infavorable conditions, though manifestly 

 due in large measure to the perfection of their arrangements for 

 preventing excessive transpiration, is also to be attribnted to a 

 remarkable combination of favorable struetures and habits. The 

 close relation existing between rate of transpiration and available 

 soil moisture was demonstrated in the ease of varions species in 

 aecordance with results previously obtained by Aloi and Feruzza, 

 and experiments to determine the relation relative efficiency of 

 several methods of supplying water to the roots of the same plants 

 have been carried out with definite results. In 1904 — 1905 Pro- 

 fessor Spalding, under a grant from the Carnegie Institution, 

 condueted an investigation regarding the absorption of water and 

 water vapor by the leaves and shoots of desert plants. It was 

 found that different species dift'er widely in their capacity for sub- 

 aerial absorption. It does not appear that this is of direct physio- 

 logical importance, though it may become an advantage indirectly 

 by preventing excessive transpiration, and may even result in leaf 

 formation, as was shown by Lloyd in the case of Fouquieria. 

 This work has been continued through the early part of the pre- 

 sent year during which a more comprehensive study, including 

 certain habitat relations of plants growing in the vicinity of the 

 Desert Laboratory, had been in progress. 



F. E. Lloyd spent two summers at the Laboratory which 

 were oecupied in a study of the physiology of stomata, and this 

 work is now being continued in residence. The plants examined 

 in particular are the Ocotülo (Fouquieria splendens) and a verbena 

 ( V. ciliata). It has, in the first place, been found possible to pre- 

 serve stomata in their natural form so that the size of the openings 

 may be studied with great exaetitude. The result of the work 

 may be summarized as follows, all Statements applying to both 

 plants except when otherwise mentioned. 



The rate of transpiration is not controlled, except perhaps 

 with in broad limits, by the size of the stomatal openings. Very 

 marke d changes in the rate either increasing or decreasing it, may 

 oeeur without any a preciable change in the stomata. It is there- 

 fore to be concluded that in these plants the stomatal mechanism 



