1 goo- 1 . ] 



Effects of Water on Foliage Leaves. 



303 



former as non-poisons. Among the poisons, CUSO4 was the most 

 deadly. With dilute solutions it always rendered the leaf quickly limp, 

 commencing at the margins. With strong solutions there seemed to be 

 a complete " paralysis," the whole leaf becoming wilted in a very short 

 time. With HgCl._, the action took place from the base outwards, 

 showing that the solution made its way out laterally from the vein only 

 with great difficulty, while the CUSO4 seemed to penetrate the whole 

 leaf rapidly, causing a wilted condition but no discolouring. 



The experiments with the sugars are of little importance, because of 

 the fact that a fermentation took place quickly, and the solution became 

 a solution of an organic acid, resulting from a decomposition of the 

 sugar. The grape sugar, as might be expected, was much more suscep- 

 tible to fermentation than was the cane sugar. 



Certain of the salts, notably ZnSOi, produced a depression of the 

 surface in spots, due to a decrease in the turgor at that point, generally 

 without that " water-logged " appearance so common in cases where a 

 leaf is being killed^ by osmotic action. 



The cause of the 

 ■" water-logged " ap- 

 pearance seen in the 

 case of certain non- 

 poisonous, but strong- 

 ly osmotic substances, 

 is due to the fact that 

 these salts in solution 

 upon reaching the 

 thin walled paren- 

 chyma cells in the 

 leaf, draw water os- 

 motically from the 

 cells into the inter- 

 cellular spaces, at first 

 in the region between 

 the main veins. In 

 some cases this is 

 noticed at the margin 

 of the leaf, but the 

 drying action of the air upon the water drawn into the intercellula 

 spaces, causes the leaf to become crisp and dry along its margin. 



The salts ascend readily into the leaf and penetrate the whole blade, 



FIG. 9. 



A, filter paper cut in the form of a leaf, it is saturated with 

 ferric chloride, and then placed in a solution of potassium ferrocya- 

 nide ; P, a precipitate ; Z, a zone of water ; B, saturated with 

 potassium sulphocyanide, and then placed in a solution of ferric 

 chloride ; a, dilute solution ; b, strong- solution ; c, partially soluble 

 in excess ; d, wholly soluble in excess ; M, margin of area if a living: 

 leaf be used. 



