1900-1.] Effects of Water on Foliage Leaves. 247 



substances, has quite recently become a prominent one with experiment 

 stations, and this question has thrown much light upon the subject 

 directly under discussion ; for it has been shown that certain poisonous 

 solutions may kill some plants and actually promote growth in others. 

 Some experiments have been performed with this end in view, — notably 

 Wales (1900), Foulkes (1897) and Bollery (1899). The object of these 

 investigators was to find a solution which when sprayed on the leaves 

 of a grain crop, would kill the weeds and not injure the grain. The 

 weed most troublesome was Brassica sinapistruin which occurs so com- 

 monly in grain fields. They found that a 2^/^ solution of CUSO4 would 

 kill the mustard and, not only not injure the wheat or oats, but actually 

 increase the yield at harvest. Other experiments have been performed 

 within the past year, both at Ottawa, Ont., and Guelph, Ont., as well as 

 in England and France, with similar results to those obtained by the 

 authors just mentioned. 



The matter of the destruction of weeds in gravel walks and waste 

 places is not so important, though some work has been attempted with 

 this end in view. Jones and Orton (1899) used several substances such 

 as NaCl, CUSO4, arsenic, kerosene, carbolic acid, etc., and found 

 carbolic acid and sodium arsenate the best. Superphosphates were 

 found by Mazieres (1899, p. 851) to be very effective in killing some 

 Cruciferous plants, while ammonium sulphate and other salts were tried 

 with varying results. 



It will be seen at a glance that this physiological problem is being 

 pressed forward from its economic, rather than from its scientific side ; 

 and that it is only within the last few years that attention has been 

 drawn to the fact that an increase in growth resulted in some cases 

 from the application to leaf surfaces of substances in solution. There 

 are many experiments, if the records are trustworthy, which prove 

 beyond a doubt that a spray of certain solutions may increase the 

 growth of plants ; but there are several views as to the real cause of the 

 increase — (i) it may act as a stimulus pure and simple — (2) it may act 

 upon the soil and through this upon the roots — (3) it may be absorbed 

 as food by the leaves. The experiments described in this paper aim at 

 answering this question. 



