POROUS CONES FOR AUTO-IRRIGATION 207 



These cones are generally more sensitive in their responses to al- 

 terations in the moisture content of the soil around them than are 

 vertically placed cylinders, and the improved form is desirable 

 whenever it is requisite to maintain the soil moisture condition 

 with as great precision as possible. The cones should be used, 

 also, in experiments in which rather careful measurements are to 

 be made of the rates of loss of water from irrigator to soil. 



For the ordinary culture of plants, where detailed measure- 

 ments of the rates of w^ater absorption by the soil are not needed 

 and w^iere considerable fluctuations in the soil moisture content 

 do not need to be specially avoided, the original cylindrical form 

 of irrigator cup is quite satisfactory, ^n such cases it is well to 

 employ as many as four or five of the regular "soil cups" furnished 

 by the Plant World, for a single cylindrical soil container about 

 15 cm. in diameter and in height. In such cases, and where 

 several of the new cones are to be operated together in the same 

 instrument, the several units are of course to be connected to- 

 gether in series, by means of bent glass, hard rubber or metal 

 tubes, so that all can be filled and emptied through the same pair 

 of main tubes. Each cup is closed by a rubber stopper bearing 

 two tubes, one of which does not reach inward beyond the stopper 

 ^\hile the other reaches to the bottom of the cup (if it is desired to 

 empty the system from time to time) . The first tube of one unit 

 is continuous with the second of the next unit in the series. At 

 one end of the series, the shorter tube terminates above with a 

 stop-cock or other means of opening and closing. At the other 

 end of the series the longer tube is j oined to the reservoir, either 

 directly or through the U-tube of a mercury barostat. Suction 

 at the open stop-cock results in filling the whole system from the 

 reservoir, after which the cock is closed. It is well to open the 

 cock from time to time and test the system for contained gas 

 by suction; if there is any gas in any of the cups it will thus be 

 removed. When -the system is to be emptied, without disturbing 

 the culture, the cock is opened and slight air pressure is applied, 

 forcing the water out through the supply tube. A little water of 

 course always remains in the cups after this operation, but this 

 will soon be removed to the soil. Readings are of course ob- 



THE PLANT WORLD, VOL. 21, NO. 8 



