NUTRITION 95 



ous at a concentration of 1%, magnesic chloride at 0.8%, 

 but they occur in sea water only to the extent of 0.75% 

 and 0.6% respectively. For strand plants the propor- 

 tions of common salt are very different, as these figures 

 indicate : 



For these three plants 3% of magnesic sulphate, 2.5% of 

 magnesic chloride, are poisonous. From these figures it is 

 obvious that strand plants are very accurately adapted to 

 the amount of common salt to which they are exposed, and 

 that they can withstand much more of the other salts than 

 they are ever exposed to.* 



The soluble compounds of zinc are poisonous to all plants. 

 In quantities not excessive M'hen first encountered, or in 

 amounts to which the special plants have become accus- 

 tomed by long habit, zinc salts seem either to be ineffective 

 or else to act as stimulants to more active growth and 

 life.t It is claimed that there is a flora characteristic of 

 soils rich in zinc. This is an exaggeration, but it cannot be 

 denied that certain plants are found on zinc soils and not 

 elsewhere (e. g. Viola calaminaria and Tblaspi calami- 

 narium ) . These, however, are varieties of other species ( viz. 

 of Y. lutea and T. alpestre), the variation being induced by 

 the poison, t 



Aluminum salts, though of very general occurrence, are 



* Schimper claims (L. c. pp. 98-102) that plants living in soils rich in 

 freely soluble salts like sodic chloride, saltpeter, etc., present structural and 

 other characters almost identical with those of desert plants. This he re- 

 gards as evidence that halophytes as well as xerophytes seek to reduce 

 transpiration, the latter because of the scarcity of water, the former be- 

 cause of the presence in it of poisonous compounds. 



t Richards, H. M. Beeinflussung des Wachsthums einiger Pike durch 

 chemische Reize. Jahrb. f. w. Bot., Bd. 30, 1897. 



X Schimper, A. F. W. Pflanzengeographie auf physiologischer Grundlage, 

 Jena, 1898. 



