PECAlSr EOSETTE. 5 



iron sulphate evokes a development of chlorophyll and at least a 

 temporary resumption of growth. 



Grape chlorosis may also result from this same set of causes and 

 in such cases responds to the ferrous-sulphate spray treatment. 

 According to Maze (53), grape chlorosis may also result directly 

 from excessive absorption of lime, and in other cases from a defi- 

 ciency of sulphur in the soil due to lowering of its availability by the 

 action of lime. Furthermore, as a result of water-culture experiments 

 he found chloroses of maize due to lack of both iron and sulphur. 

 Chlorosis in maize was also experimentally induced by the addition 

 to the solutions of various toxic substances, such as lead or methyl 

 alcohol. 



The overabsorption of lime was reported by Clausen (22) as caus- 

 ing a chlorosis of oats in Europe. 



These plant relations to various salt constituents of the soil bring 

 up the questions of plant absorption, antagonism, and changes in per- 

 meability investigated more recently by Loeb, Osterhout, Brooks, 

 Waynick, and others. As the result of a careful series of experiments 

 Waynick (83) concluded that no " optimum calcium-magnesium 

 ratio " appears to exist and that a balance between all ions present 

 in a solution appears to be far more important than any single ratio. 

 He found by chemical analysis that the composition of plants in inor- 

 ganic constituents may be enormously altered by variations in the 

 surrounding medium. The permeability of the plasma membrane 

 appeared to be changed by the nature and balance of the solution 

 around the roots. The same salt was found to act differently at differ- 

 ent concentrations, preserving the normal permeability at certain con- 

 centrations but at other strengths allowing a large penetration. With 

 regard to each salt tested, its presence in toxic concentration always 

 resulted in increased permeability of the plant tissues to calcium and 

 magnesium. On the other hand, normal growth was always accom- 

 panied by an approximately equal percentage of calcium and magne- 

 sium in the plants tested ; and in nearly all cases where growth was 

 markedly decreased the amounts of calcium and magnesium were 

 greatly increased in the tissues. The degree of absorption of any 

 salt seemed, over a wide range, to be independent of the concentra- 

 tion present; and growth was the same under widely varying ratios 

 of calcium and magnesium. The findings of Loeb, Osterhout, and 

 Brooks were confirmed in that antagonistic salt action tends toward 

 the preservation of normal permeability. 



It will readily be seen that there are many closely intergrading 

 steps or degrees of environmental effects. These are — 



(1) The adaptations without visible changes in structure or metabolism. 



(2) The general adaptive changes in anatomy or physiological processes in 

 response to physical or chemical stimuli from without. 



