THE ATMOMETER 



Is well known as a simple and efficient instrument for the measurement of 

 evaporation. Its readings are a measure of the combined effect of humidity, 

 temperature, and wind, and as such are of great value in all laboratory and field 

 work that requires an estimation of the differences in these factors as affecting 

 plant activities in different situations. 



The Atmometer cup may be used to maintain high humidities in experimental 

 work; to provide a constantly moist surface for germinating spores or growing 

 algae, fungi and protonemata; for making Pfeffer osmometer cells; and for ordi- 

 nary pressure filters. When imbedded in the soil and fed with water by tubing, 

 the cup is capable of maintaining constant degrees of soil moisture, either in the 

 open or in pots and greenhouses, the degree of moistness being determined by 

 the nature of the soil and by the height of the cup above the supplying reservoir. 



The Atmometer was devised by Dr. B. E. Livingston, Professor of Plant 

 Physiology in The Johns Hopkins University, and its adjustment, operation, 

 and scope of usefulness have been treated in the following articles in The 

 Plant World: 



Vol. 10, No. 12, p. 269 Vol. 13, No. 5, p. Ill Vol. 18, No. 2, p. 21 



Vol. 11, No. l,p. 1 Vol. 13, No. 9, p. 220 Vol. 18, No. 3, p. 51 



Vol. 11, No. 5, p. 106 Vol. 14, No. 4, p. 96 Vol. 18, No. 4, p. 95 



Vol. 13, No. 4, p. 79 Vol. 18, No. 1, p. 7 Vol. 18, No. 5, p. 143 



The Plant World now supplies the following types of Atmometer Cups: 



NATURAL CUPS. In the well-known cylindrical form, with smoothly ground 

 surface. For general purposes. 



Apiece $.50 per ten $4.00 



COATED CUPS. Glazed at base, with permanent numbering. 



Apiece $.60 per ten $5.00 



STANDARDIZED CUPS. Numbered, shellacked at base and calibrated to 

 Livingston cylindrical standard. 



Apiece $1.00 per ten $7.00 



STANDARDIZED CUPS. Numbered, glazed at base and calibrated. 



Apiece $1.15 per ten $8.00 



INSOLUBLE CUPS. Of same form as the preceding, but made of specially 

 resistent material. Numbered and standardized. Especially valuable as per- 

 manent standards for those intending to do their own standardizing. 



Apiece $2.00 per ten $18.00 



SOIL CUPS. Used cups unsuitable for atmometers but still just as good for 



auto-irrigators. When in stock. 



Apiece $.35 per ten $3.00 



Cups which have been used will be restandardized for 25 cents each; reground 

 and standardized for 40 cents. 



THE PLANT WORLD .\ TUCSON, ARIZONA 



