18 



THE PHYSIOLOGICAL ROLE OF HALOGEN COMPOUNDS. 



PLANTS RAISED WITHOUT CHLOEIDS. 



The chloriue comi)ouuds to be considered in this connection are 

 essentially those of sodium and potassium.^ These chlorids are not 

 necessary in the physiological functions of lower organisms. Fungi 

 and fresh-water algse can be successfully cultivated without a trace of a 

 chlorid. In the case of the higher plants, Knop and Batalin success- 

 fully cultivated even halophytes in the absence of sodium chlorid, and 

 Knop'^ maintains that chlorids are superfluous for all plants, and hence 

 recommends a culture fluid free from chlorids.' On the other hand, 

 functions appear, in certain plants at least, which perhaps by adapta- 

 tion become dependent upon the presence of chlorine, esj^ecially in the 

 form of potassium chlorid. 



VALUE OF POTASSIUM CHLORID FOR BUCKWHEAT. 



Nobbe has observed that buckwheat plants thrive normally in cul- 

 ture solutions without chlorids until the flowering i^eriod is over, but 

 that soon thereafter the tips of the stalks die off"; the upper part of 

 the stalk thickens and shows ring-like swellings; the epidermis bursts 

 vertically; the dark green leaves become brittle, spotted, and pufly, 

 and roll in; no fruit is produced;^ and a microscopical examination 

 shows a great accumulation of starch granules in parts of the stems. 

 These observations have been confirmed by Leydhecker.^ 



It might be supposed that the formation of diastase is prevented by 

 the absence of chlorids, and that the transportation of starch thus 

 becomes impossible, but the difficulty interposed by this hypothesis is 

 that the development of the plant proceeds normally for a cousiderai)le 

 length of time, that is, until the flowering stage is reached. This also 

 militates against Detmer's belief that the beneficial action of potassium 

 chlorid on the migration of starch is due to the formation of hydro- 

 chloric acid from this chlorid,'' which acid he claims will in very small 

 quantities promote the saccharification of starch by diastase. 



'Calcium and magnesium chlorid have an injurious effect on plants, probably on 

 account of the liberation of hydrochloric acid in cells, this not being assimilated like 

 nitric or sulphuric acids and therefore accumulating to a noxious degree. 



^Kreislauf des Stoffs, Vol. I, p. 616. The writer can testify that when 0.01 per 

 cent of sodium or potassium chlorid is added to suitable complete culture solutions 

 no essential difference in growth or the amount of starch will be noticed in the 

 cells of Spirogyra, but 0.5 per cent will retard growth. 



^In Knop's culture fluid the proportion of the mineral nutrients is as follows: 

 1 KXO:j, 1 KH0PO4, 1 MgSOj, and 4 Ca(N03)2. The iron is suspended as ferric phos- 

 phate. 



^All these phenomena have been observed by the writer in the case of buckwheat 

 plants which received rubidium nitrate, and to a smaller degree also when rubidium 

 chorid was used (p. 24). 



sLandw. Vers. Stat., 1865 and 1866, Vols. VII and VIII. 



''Pflanzeni)hy8iol, Unters. liber Fermentbildung, Jena, 1884. 



