THE PERMEABILITY OF PROTOPLASM 131 



diminished without injury. A rapid alternation of increase 

 (amounting to 20 per cent, above normal) and decrease 

 (amounting to 39 per cent, below normal) failed to 

 produce any evil effects. 



He has also (1915, 2) drawn attention to the remarkable 

 difference between monovalent and bivalent kations in 

 their effects on permeability. While none of the mono- 

 valent kations except hydrion are able to decrease per- 

 meability, all the bivalent kations so far investigated are 

 able to do so to a marked degree. These include the 

 bivalent ions of magnesium, calcium, barium, strontium, 

 manganese, cobalt, iron, nickel, zinc, cadmium, and tin. 

 Furthermore, he has demonstrated (1915, 3) that the 

 trivalent kations of lanthanum, cerium, yttrium, iron, 

 aluminium, and the tetravalent kation of thorium, are 

 all able to decrease permeability to a considerable extent. 



THE EFFECT OF ALTERATIONS IN TEMPERATURE 

 UPON PERMEABILITY. 



This subject has recently been investigated by Eckerson 

 (1914), and the results obtained lead to the conclusion 

 that thermotropism is intimately connected with altera- 

 tions in permeability, and consequently in turgor. 



Rysselberghe (1901) had previously shown that the 

 permeability of epidermal cells of Tradescantia discolor to 

 dissolved substances such as glycerol, carbamide, and 

 potassium nitrate, increases with rise of temperature from 

 to 30. Lepeschkin (1905), working with another plant, 

 found an increase of permeability from to 20, and a 

 decrease from 20 to 35. This worker also proved that 

 the permeability of protoplasm to sucrose does not change 

 within a moderate range of temperature, though that of 

 potassium nitrate increases, as a consequence of which 

 higher concentrations are necessary to bring about plas- 



