THE POROUS CUP ATMOMETER 



Is the most simple and efficient instrument ever devised 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 kinds of botanical, agricultural, and horti- 

 cultural operations which require an estimation of the differences 

 in these factors as affecting plant growth in different situations. 

 Its installation requires only the use of a jar, corks and tubing as 

 described in the first article referred to below. 



The atmometer may also be used to maintain high humidities 

 in experimental work; to provide a constantly moist surface for 

 germinating spores or growing algae, fungi and protonemata. 



When immersed in the soil and fed with water by tubing, 

 the atmometer cup is capable of maintaining constant degrees of 

 soil moisture, either in tfie open or in pots and greenhouses, the 

 degree of moistness being determined by the height of the supplying 

 reservoir above the soil. 



This type of atmometer cup was devised by Dr. Burton E. 

 Livingston, Professor of Plant Physiology in 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. 4, p. 79; 



Vol. 11, No. 1, p. 1; Vol. 13, No. 5, p. Ill; 



Vol. 11, No. 5, p. 106; Vol. 13, No. 9, p. 220. 

 We are able to supply the atmometer cups in the NATURAL 

 state for use in soil orfor cultures, COATED AT THE BASE for 

 use in measurement of evaporation; or COATED AND STAND- 

 ARDIZED for careful climatological and ecological work in 

 which it is desirable to know the value of the readings obtained 

 in terms of the adopted standards which have already been widely 

 used. Our prices for these types are: 



NATURAL CUPS apiece $ .50. .per 10 $4.00 



COATED AT BASE " .60.. " 5.00 



COATED and STANDARDIZED. " 1.00.. " 7.00 

 SOIL CUPS (seconds) when in stock. " .35.. " 3.00 



Cups which have been used will be restandardized at 25 cents 

 each; Reground and standardized at 40 cents. 



Eastern orders are supplied from Baltimore; western from 

 Tucson. 



THE PLANT WORLD, Tucson, Arizona 



