DEPARTMENT OF BOTANICAL RESEARCH. 75 



in greater proportion and vary more widely through the day than in 

 the large echinocacti. Some connection with the hydratation of the 

 slimes or mucilages is suggested. 



Isolated individuals of succulent species survive varying periods 

 when separated from a moist substratum. If the conditions for photo- 

 synthesis are inadequate, death may result from starvation. The 

 disintegration of solid material in diffuse light may be such that the 

 proportion of water in the tissues may be but little changed after 

 several j'ears of depletion. 



SOME SPECIAL WATER RELATIONS OF PLANTS. 

 Plane Porous Clay Surfaces for Use in Atmometry, by B. E. Livingston. 



The first porous-cup atmometer to be described was that of Bellani 

 (1820), who employed what was essentially a porous cup with a plane 

 circular upper surface and with the remainder of the wall impervious 

 to water. The evaporating surface was that of a circular disk of porous 

 clay closing the top of a metal cylinder, the latter filled with distilled 

 water and connected to a reservoir below. This form of surface is 

 exposed in practically the same manner as is a free water surface, yet 

 the Bellani type of instrument encounters none of the difficulties met 

 with in the operation of open pans of water. Nevertheless, this form 

 of atmometer has failed to attract attention. 



After some experimentation a satisfactory form of Bellani plate has 

 been obtained, consisting of a circular disk of white, porous porcelain, 

 77 mm. in diameter, mounted across the large end of a glazed porcelain 

 funnel. The apparatus is made as a single piece, the funnel and the 

 disk being continuous and of the same material, but the lateral surface 

 is heavily glazed externally. Wherever atmometric studies are to be 

 related to water-loss from plane surfaces this modification of the porous 

 cup may be employed. 



Influence of Solar Radiation as a Drying Agent, by B. E. Livingston and 



E. S. Johnston. 



Further progress toward the obtaining of satisfactory black porous 

 spheres for the radio-atmometer has been made and a small number of 

 usable pieces have been available for the summer of 1915. The black 

 spheres heretofore obtained have generally proved unsatisfactory in 

 various ways, and experimentation in the manufacture of these difficult 

 pieces is being continued. 



The records furnished by the radio-atmometer (a wliite and a black 

 sphere operated side by side) in the open and in various intensities 

 of shade have been critically studied for the summer climate of Balti- 

 more and for that of Tucson. The instrument proves to be consider- 

 ably more sensitive to the drjdng action of sunshine than is any plant 

 so far tested, and it promises to be amplj- sensitive for ecological studies 

 of solar radiation as a desiccating influence. 



