AGRICULTUR.\L BOTANY CHEMISTRY AND PHYSIOLOGY OF PLANTS 1757 



b) Knop's " acid " culture solution containing per litre : 



Calcium sulphate 1.12 gm. 



Ammonium sulphate 0.45 



Sodium nitrate 0.42 



Potassium phosphate 0.27 



Potassium chloride 0.15 



Magnesium sulphate 0.12 



Ferric phosphate 6.20 



These were modified according to the scheme given below. 



i) Knop's normal culture solution 



In all cases where carbonates were present chlorotic plants were ob- 

 tained, the effect of the three carbonates being identical. When a very lit- 

 tle phosphoric acid was added, a green colour appeared at the base of the 

 topmost leaves. The amount added was sufficient to give the nutrient me* 

 dium an acid reaction, and in a later set of experiments the phosphoric 

 acid was replaced by hydrochloric, sulphuric and nitric acids with the same 

 result, showing that the antichlorotic action was due to the acidity of the 

 solution and not to the presence of phosphorus. The exclusion of magne- 

 sium had no appreciable effect on chlorosis, but the plants without sulphur 

 were affected though not quite in the manner described by Maz6. Ac- 

 cording to the latter, chlorosis caused by the absence of sulphur is identi- 

 cal with chlorosis caused by the absence of iron, whereas in the present 

 experiments, sulphur chlorosis was somewhat later in appearing and the 

 colour of the leaves was never quite the same in the two cases. 



For the sand cultures the same scheme was adopted as for the water 

 cultures but Hellriegel's nutrient solution was substituted for Knop's. 

 Pots with a capacit}' of 4 ^ litres were used. The results obtained were 

 somewhat different from those of the water cultures and this was attribut- 

 ed to the nature of the medium which was never quite neutral. 



The phenomenon of chlorosis was then studied in greater detail b}' the 

 method of " isolated nutrition " or in other words by dividing the root 

 system into two parts, one of which received the iron alone, or iron and car- 

 bonate alone, and the other the re.st of the food solution. Where a car- 

 bonate was added, chlorosis appeared as before, but where iron was used 

 alone, variegated leaves were obtained. In the majority of cases one half 

 of each leaf was yellow and the other half green, but sometimes there was 

 a green band in the middle with yellow on either side, or the leaf might 



