24 PHYSIOLOGICAL ROLE OF MINERAL NUTRIENTS. 



hand be injurious to the chlorophyll, while on the other hand they 

 may exert a beneficial action by stimulating growth of the plant. 

 When these compounds are supplied in a sufficiently high degree of 

 dilution only the beneficial action is exerted. This may be of some 

 practical value on soils where manganese in readily available condition 

 is wanting. 



Nagaoka has recently observed in a field experiment with rice an 

 increase of one-third of the harvest after adding manganous sulphate 

 to the soil at the rate of 50 kilos per hectare. 



THE PHYSIOLOGICAL, ROLE OF HALOGEN COMPOUNDS. 



PLANTS RAISED WITHOUT CHLORIDS. 



The chlorin compounds 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 alga? 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 5 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 b} T adapta- 

 tion become dependent upon the presence of chlorin, especially 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 period 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 puffy, 

 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 



a 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. 



c In Knop's culture fluid the proportion of the mineral nutrients is as follows: 1 

 KN0 3 , 1 KH 2 P0 4 , 1 MgS0 4 , and 4 Ca(N0 3 ),. The iron is suspended as ferric phos- 

 phate. 



^Landw. Vers. Stat., 1865 an. 1 1886, \~n\s. VII :\r. 1 VIII. 



