Lloyd, The Desert Botan. Laboratory of tho Carnegie Instit. of Washington. 797 



of the most interesting generalizations obtained set forth the facl 

 that plants with storage organs for water were given highly cha- 

 racteristic of arid regions in which the total precipitation occurs 

 within a very short period each year, these struktures being noti- 

 ceably absent from plants of regions which receive a scant ra in fall 

 redistributed in small quantities tbroughout the year. 



Dr. W. A. Cannon came to the Desert Laboratory as Resi- 

 dent Investigator in the autumn of 1903 and since then has been 

 engaged on studies on the transpiration and the structure of the 

 desert plants in the vicinity of the Laboratory. Sonie of the re- 

 sults of the studies on transpiration may he hriefly presented. 



By a method perfected at the Laboratory 1 ) the transpiration 

 of plants was observed at different seasons while they were growing 

 undisturbed in their habitats. Aniong other things it was learned, 

 other things being equal, that a marked acceleration of rate took 

 place with an increase in the available water supply. This was 

 noted in leafless as well as in leafy fornis, and in the latter with 

 or without an increase in the area of the transpiration surface. 

 The Variation in rate between seasons of extreme drought and 

 seasons of rain was very marked particularily in leafy forms. 

 In Fouquieria splendens, for instance, the ratio was 1 : 32. But in 

 the leafless plants it was inuch less. The highest rate noted for 

 the leafy condition of the leafy forms of typical desert perennials 

 was quite as high as the rate of the desert annuals or of such 

 mesophytic plant as the sugar beet. The minimum of the former, 

 however, is probably much more than that of the latter class. 



In addition to work on independent plants some observations 

 were made on the transpiration of the parasitic Phoradendron and 

 its hosts. The rate of transpiration of the mistletoe is frequently 

 greater than that of the host. The studies show, however, that the 

 rate may be a variable one, being higher near the main stem of 

 the host than more remote from it. That is, the Variation may be 

 associated, as is the case in the independent plants, with the 

 Variation in the water supply. 



Under a grant from the Carnegie Institution Dr. B. E. Li ving- 

 ston spent the major portion of the summer of 1904 at the La- 

 boratory, studying the moisture conditions of the soil and atmo- 

 sphere, under which desert plants" are obliged to exist during the 

 summer season. A summary of this work may be given as follows. 

 1. The deeper soil layers of the hill on which the Laboratory 

 Stands contain at the end of the dry season, and thus probably at 

 all times, a water content adequate to the needs of those desert 

 plants which are active through the months of drought. This con- 



1) Bull. Torr. Bot. Club, 32 : 515. 1905. 



