3o8 •' Transactions of the Canadian Institute. [Vol. VII. 



Solutions do not ascend through the blade of the leaf as they do 

 through filter paper (Photos. i-6, and Fig. 9). 



The lithium test for the rate of ascent of water is not accurate for 

 filter paper, and may not be therefore, for plants. 



Detached leaves may carry on some of their normal functions for a 

 long period of time. 



VIII. — On the Effect of a Solution Applied to the 

 Leaf Surface. 



This introduces one of the most important phases of the subject, and 

 one towards which the attention of the fruit-grower and the farmer has 

 been directed for the last decade or more. Since the protecting of 

 plants from the ravages of fungi and of insects has been attempted by 

 means of spraying with liquids of a more or less poisonous character, 

 the attention of many, especially of those in experiment stations, has 

 been turned towards the increase or decrease in crop, owing to the 

 application of the poison, in solution, to the leaf of the plant. Some 

 experiments have been carried on, notably at the Agricultural Experi- 

 mental Station, Ottawa, 1900, with a view to the extermination of 

 weeds by spraying. The experiments performed by the writer, and here 

 described, show, as has been shown elsewhere, that leaves of plants are 

 affected differentl}' by the same solution. What one leaf will endure 

 will kill another; and taking advantage of this fact, plants susceptible to 

 the solution may be destroyed. It has recently been learned that the 

 common field grains, such as wheat, barley and oats, are well adapted to 

 the shedding of drops applied in the form of a spray, because of the 

 chemical nature of the surface, because of the shape of the leaf and of its 

 natural position with regard to the stem. 



Probably the most troublesome weed now in many parts of the 

 northern United States and Canada, is the wild mustard (Brassica 

 sinapistrim, Boiss.) ; and the means just referred to have been success- 

 fully used towards its extermination. A spray of a solution of 

 CUSO4 and of FeS04 have been used with singular effect, and a certain 

 strength of solution was found which would kill the mustard and not 

 materially injure the grain crop. At Ottawa it was found that the 

 solution of FeSOi of 10% strength produced some "scorching" of the 

 barley, but stripped the mustard of its leaves and " scorched " the stem 

 to some extent, but did not completely kill it. The 2% CUSO4 solution 

 produced only a slight injury to the barley crop but completely killed 



