110 



WATER-ABSORPTION AND TRANSPIRATION. 



1 oz. each of potassium nitrate (saltpetre), magnesium sulphate (Epsom 

 salt), and potassium phosphate, and powder these salts to make them 

 dissolve more readily. These quantities will be sufficient for 32 gallons 

 of culture solution ; but the latter should be made up as required, so 

 that the above quantity of each salt should be subdivided according to 

 the volume of solution required each time. 



Another method is to prepare strong solutions of the salts and dilute 

 them as required. Make (1 ; a solution containing 2 grammes Ca(N0 3 ) 2 , 

 1 gramme KN0 3 , and 1 gramme KH.,P0 4 to every 100 c.cs. of water ; 

 (2) a solution containing O'o gramme MgS0 4 to every 100 c.cs. of water. 

 Grow seedlings of Bean, Pea, Maize, Buckwheat (these answer well, 

 but other plants should be tried, different plants each time you start a 

 series of cultures) until the roots have grown 

 a few inches long, then fix each seedling into a 

 cork or a wooden cover. The cork or cover 

 should have a hole in the centre for the plant, 

 a slit somewhat narrower than the hole running 

 to the edge of the cover (so that the plant can 

 be removed easily when necessary), and another 

 hole for a stick to tie the plant to (Fig. 39). 

 Take care to keep the cork, or wooden cover, as 

 well as the part of the plant which is in contact 

 with it, quite dry ; most failures in water- 

 culture are due to "damping off" at this part 

 (caused by fungi). If a stick is used to support 



the plant, there is no need for any packing material. Cuttings of 

 Willow and other trees may be used as well as seedlings. 



Darken the roots by covering the jars with black cloth or paper ; 

 add water each day to*replace that lost by evaporation and transpiration 

 (using a funnel, and not letting the cork, or wood cover, get wet). Once 

 a month take the plant out, wash its roots gently in a oasin of water, 

 pour out the culture solution, and let the plant remain with its roots 

 in plain water for two days before placing it into fresh culture solution. 

 The culture solution should not be alkaline, or the roots suffer ; if it 

 turns red litmus to a blue colour, add acid (e.g. phosphoric acid) until 

 it gives an acid reaction. 



The roots should be supplied with air ; the simplest plan is to force 

 air into the solution every day or two with a bicycle-pump or a con- 

 densing syringe. Plants in culture solutions are apt to suffer badly 

 from lack of oxygen, the amount of which is far below that present in 

 a well-aerated soil. If possible, use vessels of 1 gallon capacity. 



Fig. 39. 



* 145. Experiments with incomplete Culture Solutions. 



Choose seedlings as nearly equal in size and general growth as possible, 

 then place some in a complete solution, others in a solution from which 

 one or other of the essential elements is wanting. To deprive the 

 plant of potassium, use sodium nitrate instead of potassium nitrate, 

 and calcium phosphate instead of potassium phosphate. Deprive 

 others of calcium by omitting the calcium nitrate ; of phosphorus by 

 omitting the potassium phosphate ; of magnesium by using calcium 



