THE FOOD OF PLANTS. 63 



quartz. On this we put a thin layer of unsized cotton wool, and 

 fill the cylinders with a quartz sand, the particles of which are 

 mostly G'2-0'4 mm. in diameter.* Before being filled into the 

 cylinder, the sand is prepared as follows: Every kilogramme of 

 dry sand to be used is mixed with 4 gr. of Calcium carbonate, 

 O'loO gr. of Potassium phosphate, O070 gr. of Potassium chloride, 

 O070 gr. of Magnesium sulphate (the last three salts dissolved in 

 150 c.c. of water) and a little phosphate of iron. The sand is now 

 in the moist state crumbled into the cylinders and gently pressed 

 down from time to time. The same quantity of sand is intro- 

 duced into each cylinder. For investigation we select oats arid 

 peas. The seeds must be very normal and of medium weight. 

 They are germinated between folds of blotting-paper, and the 

 seedlings are put into the sand, twelve oat seedlings or six pea seed- 

 lings to each cylinder. After a time we remove six out of every set 

 of twelve oat seedlings, and three out of every six pea seedlings, 

 taking great care that remnants of seed and roots are not left 

 behind in the sand. The cylinders are now left with six of the 

 best developed oat seedlings or three pea seedlings. The latter 

 are at once provided with supports. The cylinders are set in a 

 sunny position in the garden, being brought under cover only in 

 rain or strong' wind, or on very hot days. Every day the cylin- 

 ders are weighed, and the water lost by evaporation is replaced. 

 Besides the cylinders whose sand did not receive any admixture 

 of nitrogenous compounds, we prepare others in which we further 

 add to the sand 2'00 gr., T50 gr., I'OO gr., 0'50 gr., or O'lO gr. of 

 Calcium nitrate. f In the course of the summer it is found that 

 the oats unprovided with Calcium nitrate thrive at best poorly, 

 while the power of elaborating material grows considerably with 

 increase in the quantity of nitrate in the soil, and keeps pace with 

 this increase. In the pea cultures on the contrary no exact rela- 

 tion is perceptible between the quantity of nitrate present and 

 the capacity for growth, indeed it appears that the peas develop 

 very vigorously even when nitrates are absent from the soil. By 

 comparing the dry weight of the plants obtained with the dry 

 weight of the seeds, we arrive at still more exact information 



A very suitable, double-washed Tertiary quartz sand from the Saxony 

 Oberlausitz, which contains so little Nitrogen that it may be neglected, is to be 

 obtained of the firm H. Weichelt & Co., Vereinigte Hohen-Bockaer Glassand- 

 gruben, Dresden. 



t These quantities are not per kilogramme of sand, but per cylinder. 



