2 PHYSIOLOGY OF NUTRITION. 



stance. This last, it is true, does not consist entirely of organic 

 bodies. There are present in it in addition mineral constituents, 

 but the quantity of these is relatively so trifling, that we may here 

 leave them out of consideration. 



For the culture experiments which are to be made, we select a 

 few fruits or seeds as perfectly developed as possible. Each of 

 these is separately weighed and the weight noted. The previously 

 made dry-substance determination now enables us to calculate 

 the dry weight of each individual fruit or each individual seed. 

 The objects are next placed separately in small glass or porcelain 

 dishes, covered with water, and left in this for twelve to twenty- 

 four hours to soak. They are then transferred to moist sawdust, 

 contained in a suitable box or flower-pot, to germinate. It may 

 here be remarked once for all that the sawdust, well soaked, must 

 be rubbed between the hands, and placed in the vessels so as to 

 form as loose as possible a seed bed. We lay the Phaseolus seeds 

 horizontally in the sawdust, so that the emergent root forms a 

 right angle with the long axis of the seed. Maize grains are so 

 laid that the emerging root can grow straight downwards without 

 making curvatures. So also we lay seeds of, e.g., Vicia Faba in 

 the sawdust with the micropyle directed downwards. When their 

 radicles have reached a length of several centimetres the seedlings 

 are cautiously removed from the sawdust, carefully washed, and 

 further developed by the method of water culture. 



For this we need in the first place suitable glass cylinders, 

 which, if we are experimenting, e.g., with maize plants, must be 

 capable of holding about 2 litres of fluid. For smaller plants 

 smaller vessels will suffice. The cylinders are filled not with 

 pure water but with a food solution, in order to satisfy the re- 

 quirements of the plants as regards mineral substances, a subject 

 to which we shall return in detail later. The food solution may 

 be prepared at once in large quantities, and kept in the dark in 

 well closed vessels. A suitable food solution is obtained by using 

 the specified quantities of the substances named below to 1 litre 

 of distilled water * 



10 gr. Calcium nitrate (Ca(N0 3 ) 2 ) ; 



0'25 gr. Potassium chloride (KC1) ; 



O25 gr. Magnesium sulphate (Mg S0 4 ) ; 

 ' 0-25 gr. Potassium phosphate (KH 2 P0 4 ). 



* It is quite sufficient to weigh out the salts by means of a small pair of 

 hand scales with horn scale-pans. 



