THE FOOD OF PLANTS. O 



To the aqueous solution of these substances we further add a few 

 drops of Ferric chloride solution. 



I have often used this food solution with much success. A 

 very satisfactory food solution is also obtained by dissolving the 

 following in 1 litre of water : 



VO gr. Potassium nitrate ; 

 ^ 0'5 gr. Sodium chloride ; 



0'5 gr. Calcium sulphate ; 

 O5 gr. Magnesium sulphate ; 

 0'5 gr. tribasic Calcium phosphate. 



The Calcium phosphate is very finely powdered before use. It is 

 very sparingly soluble in water, and consequently forms a sedi- 

 ment at the bottom of the culture vessel. The food solution is 

 completed by addition of a few drops of Ferric chloride solu- 

 tion. 



Having filled the cylinders with food solution, and selected for 

 each a suitable cork provided with a large hole, the seedlings are 

 fixed in the holes of the corks by means of cotton wool (see Fig. 1). 

 Each plant requires a separate cylinder. The roots must extend 

 into the food solution; the still present receptacles of reserve 

 material (endosperm or cotyledons) should not dip into it, but 

 still must not be allowed to dry up. The culture vessels with 

 their plants are placed in front of a window, where the latter are 

 exposed to direct sunlight. Over the cylinders however is pasted 

 black glazed paper, so as to prevent the development of alga3 in 

 the food solution and on the roots of the plants. The white side 

 of the paper must be outside, and then the fluid in the culture 

 vessels does not get too warm. A still more simple plan for screen- 

 ing the roots from access of light is to place each culture vessel in 

 a cardboard cylinder. It is obvious that as vegetation proceeds 

 care must be taken to replace frequently by distilled water the 

 water absorbed from the food solutions. 



The precautions to which attention must be paid when it is 

 desired to bring plants to an advanced stage of development by the 

 water-culture method, will be discussed later in this section. We 

 are at first only concerned in proving that green plants in general 

 can produce organic substance, and it is therefore quite sufficient if 

 they vegetate for a few weeks, and produce vigorous stems, leaves 

 and roots. We then remove the plants from the food solutions, 



