60 



PHYSIOLOGY OF NUTRITION. 



Pea and wheat plants are very suitable as research material. 

 We first provide ourselves with well developed and thoroughly 

 good seeds, and determine their dry weight and also the quantity 

 of Nitrogen they contain. 1 A few wheat grains (say 30) or pea 

 seeds (say 6) are accurately weighed. From their weight we can 

 easily determine the quantity of Nitrogen they contain on the 

 basis of the Nitrogen estimations above mentioned. The ob- 

 jects are placed in a small glass dish with a little freshly prepared 

 distilled water. The dish is left for about twenty-four hours 

 under the bell-glass of the apparatus to be described immediately, 

 and at the end of this period the small quantity of water still left 

 is poured off from the seeds and evaporated to dryness in a porce- 

 lain dish on the water-bath. The dish with the residue is placed 

 in a dessicator. The soaked seeds are now brought to further 

 development in the apparatus represented in Fig. 21. On a 

 ground glass plate stands a beaker ', over the top of which is 

 bound a piece of netting or a piece of perforated parchment paper. 

 The beaker contains a food solution made with freshly prepared 

 distilled water, and in which are present all the food stuffs except 

 Nitric acid and ammonia (see 22). The seeds are placed on the 



netting or parchment 

 paper, in place of which 

 we may use a perforated 

 silver plate, so that the de^ 

 veloping roots grow down 

 into the food solution. The 

 ground edge of the very 

 large bell - glass G is 

 cemented perfectly air- 

 tight to the ground glass 

 plate. This is best effected 

 by means of a cement pre- 

 pared by melting together 

 1 part of wax and 3 to 4 

 parts of lard. The bell- 

 glass may also be closed 

 below by placing it in a 

 large dish of mercury. The 



FIG. 21.-Apparatns for the culture of plants in p _ p ^ however 



the absence of all nitrogenous compounds. ur J 1St > ^ evei ' 



be covered with water so 

 as to prevent injury to the seedlings from the vapour of the 



