University of Colorado 

 Mountain Laboratory 



Rich and Varied Flora from plains to alpine peaks easily acces- 

 sible. Boulder (5,300 feet) is at the base of the foothills 

 and Tolland (8,889 feet) is in the montane zone. 



Courses in Field Botany, Ecology and Taxonomy. First three 

 weeks at Boulder, last three weeks at Tolland. Work 

 suitable for graduates and advanced undergraduates. 

 No elementary work given. 



Tenth Annual Session June 25 to August 3, 1918. Fees mod- 

 erate; expenses reasonable. An opportunity to learn much 

 with little expenditure of time and money. 



Additional Information may be obtained by addressing Profes- 

 sor Francis Ramaley, University of Colorado, Boulder, 

 Colorado. 



SPHERICAL ATMOMETER CUPS 



A spherical evaporating surface, 5 cm. 

 in diameter, presenting the same external ex- 

 posure in all directions, with glazed cylindri- 

 cal neck 3 cm. long and 2 cm. inside diameter. 

 They are composed of very resistant material, 

 of proper porosity for atmometric work, and 

 are to be mounted on rubber stoppers as in 

 the case of cylindrical cups. The spheres may be cleaned with brush and distilled 

 water, may be treated with acid, and even heated to red heat. They should thus be 

 capable of many years of use, without permanent alteration of the coefficient. They 

 are not easily broken. 



These new spheres are supplied either standardized or unstandardized. Stand- 

 ardization is carried out with reference to a newly adopted spherical standard; spheres 

 cannot be satisfactorily standardized to the cylindrical standard cup. Therefore 

 readings from spheres are not satisfactorily reducible to terms of readings from cylin- 

 ders (see Plant World, Vol. 18, pp. 21, 51, 95, 143). 



Unstandardized White Spheres, $2.25 each, $20.00 per ten 

 Standardized White Spheres, $2.75 each, $25.00 per ten 



THE PLANT WORLD - - TUCSON, ARIZONA 



