POROUS CONES FOR AUTO-IRRIGATION 205 



sitates that the rest of the cup, which might be conical or hemi- 

 spherical, with a projecting neck, must lie below the container. 

 Also, it is difficult to arrange for a relatively large supplying sur- 

 face in such a case, as compared with the soil volume, unless the 

 soil forms a comparatively thin layer on the horiJzontal porous 

 plate. 



Another way of attaining the desired end to a certain degree 

 is of course accomplished if a plane porous surface is placed in the 

 soil so as to face obliquely upward, but this arrangement also 

 presents difficulties that may be easily imagined, and it is not 

 generally practicable. On the whole, it appears that the most 

 generally satisfactory way to install an auto-irrigator is to employ 

 a porous cup having a conical surface, the circular base of the 

 cone resting on the bottom of the soil container, or being not far 

 above it, and the axis of the cone being vertical. This arrange- 

 ment furnishes an oblique porous surface along which the soil may 

 gradually slip downward, becoming always more effectively 

 pressed against the cup. This is particularly true when the walls 

 of the soil container also have the form of a cone, the apex point- 

 ing downward, as in the case of an ordinary flower pot. The 

 slightly inclined wall of the pot tends to throw the downward 

 moving soil laterally against the conical porous cup within. This 

 arrangement furnishes a relatively large water-supplying surface, 

 as related to the soil volume, and the surface is so exposed as not 

 only to provide good contact with this soil at all times but also to 

 lie in a practically ideal position with reference to downward- 

 growing roots, which automatically tend to approach the source 

 of water supply as they grow. 



After preliminary experimentation suitable porous porcelain 

 cones for auto-irrigation have been made available at a reason- 

 able price. They are somewhat like the Bellani plate used in 

 atmometry,- but the sloping wall is conical instead of hemispheri- 

 cal and is porous instead of being glazed. The new cones resem- 

 ble, in form, an ordinary funnel, if w^e suppose the large opening 

 of the latter to be closed by a circular plate. The whole is made of 



^Livingston, B. E., A modification of the Bellani porous plate atmometer. 

 .Science, n. s. 41 : 872-874. 1915. 



