as well as phosphoric acid. Now it is not possible to remove this nitrogen, and yet it is important that when the phosphoric acid in the bone is tested the nitrogen it contains should in no way affect the results. Therefore, if the soil does not contain an excess of nitrogen such an excess should be applied, together with sufficient potash to enable the bone phosphoric acid to be turned to full account. In this way if any increase in yield results it can be attributed to the phosphoric acid alone. DETAILS OF THE WAGNER METHOD. A description was given in the preceding article1 of the general arrangements of the greenhouses and experimental gardens. As there stated there are two greenhouses, with doors opening outward and tracks running out into the garden. On these tracks the movable pots are transported in wagons, being moved out in pleasant weather and returned to the greenhouses at night or when a storm is threatened. A more detailed description of the pots, tracks, and wagons is here given, followed by the details of the method. POTS. The pots as well as the large soil cylinders are made of zinc. The interior was formerly coated with asphaltum, but this was afterwards found to be unnecessary, the zine having no injurious effect upon the plant. The movable pots are so arranged that part of the water can be supplied from beneath. To attain this end several devices were formerly in use, but the one now preferred consists of a zinc tube about threefourths inch in diameter securely fastened to the outside of the pot, extending from the middle to the base where it opens into the bottom. A piece of sheet zinc rolled over into a semi-cylindrical form, with notches cut out on the under edges, connects with the tube opening and extends across the bottom of the pot. This arrangement prevents the water tube from getting clogged by the gravel and soil and allows the water to enter freely. An iron rim extends around the top of the pot to strengthen it, and just below the rim at equal intervals three sockets are securely soldered, into which the cage or frame fits, which is to support the plant. The pots rest upon iron legs fastened on to the outside, thus raising them about 21⁄2 in. above the surface on which they rest. Each pot must be water-tight. The cylinders which are inserted in the ground are also made of zinc, and have no bottoms. An iron rim about the top gives them stability. The Darmstadt Station has in use the following cylinders and pots: 24 embedded cylinders 100 cm. in diameter and 133 cm. deep; 360 cylinders 60 cm. in diameter and 133 cm. deep; 51 pots supported on rails, 60 cm. in diameter and 80 cm. deep; 50 pots supported on legs, 30 cm. in diameter and 33 cm. deep; 316 pots supported on legs, 25 cm. in diam 1 E. S. R., 7, p. 4. |