6 PHYSIOLOGY OF NUTRITION. 



desirable to set up a special plant house, made of glass and 

 iron, and so constructed that the culture vessels standing on 

 small trollies can readily be brought into the open as often as 

 possible. 1 * 



5. Obviously care must be taken to replace frequently the 

 water lost by the food solutions. When the plants have formed 

 a vigorous root system, it is advisable to remove them, for one to 

 two days, say, every week, from the food solutions, and transfer 

 them to distilled water. 



6. Great care must be taken to keep the food solution slightly 

 acid in reaction. An alkaline reaction, which is highly injurious, 

 may be remedied by addition of a little Phosphoric acid. 



7. To keep the roots in the food solution adequately supplied 

 with Oxygen, and prevent the formation of Ferric sulphide which 

 may take place with deficiency of Oxygen, it is advisable to pass 

 a stream of air through the food solution once or twice every day. 

 This is most simply done by means of a gasholder. The glass 

 tube conducting the air passes to the bottom of the culture vessel 

 through the third opening above mentioned of the cover. 2 



8. Very frequent renewal of the food solution is by no means 

 necessary, and not even of advantage, as experience has frequently 

 shown. As a rule it is sufficient, if we are working with culture 

 vessels of about 3 litres capacity, to renew the solution two or 

 three times in the course of the summer. It is convenient to pre- 

 pare beforehand concentrated solutions of the nutrient salts, and 

 then dilute them to the proper strength for use. For example, we 

 may dissolve in every 50 c.c. of water, 1 gr. Calcium nitrate, 

 0*25 gr. Potassium chloride, and O25 gr., acid Potassium phos- 

 phate, and in a second solution keep on hand O25 gr. Mag- 

 nesium sulphate to every 50 c.c. of water. The food solution 

 when made up will only require the addition of a few drops of 

 Ferric chloride solution. It is advisable to remove the plants 

 from the food solution when the stage of fruit ripening draws 

 near, and to supply them with distilled water only, which, if the 

 researches permit it, is very slightly acidified with Nitric or Phos- 

 phoric acid. 



At the time of flowering care must be taken that normal fertili- 

 sation takes place. It is generally sufficient to let the plants 



* It is advisable to enclose the space intended for the plants outside the 

 plant house with wire netting, so as to keep away birds. 



