2^6 Transactions of the Canadian Institute. [Vol. VII. 



a disputed question. Smith showed pretty clearly that the leaves were 

 affected directly. Schlossing (1874, P- 1700), and Mayer (1874) showed 

 that solutions of ammonium carbonate were absorbed by leaves ; and 

 Schlossing showed that the ammonia thus absorbed increased the 

 growth of the plant. Boussingault (1878) showed that calcium sulphate, 

 potassium phosphate and potassium nitrate may be absorbed by leaves 

 of plants. There is no mention made by Boussingault as to how these 

 substances affected the tissue of the leaf, or whether they proved 

 of advantage or of disadvantage to the leaf of the plant as a living 

 organ or organism. 



Cuboni sprayed leaves with lime, and concluded that it increased the 

 growth, if not by the absorption of the solution of lime, then by a 

 stimulation. In Sachs' Lehrbuch reference is made to the work of 

 Boussingault, and Sachs further states that the absorption may be 

 proved by using a soluble lithium salt, then using the flame test to 

 determine the extent of the absorption. Oliver (1893), after investigat- 

 ing the effects of urban fog upon vegetation, showed that certain acid 

 vapours and other substances affected the leaves, injuring the chlorophyll. 

 About this time investigations were made into the effects of the 

 bordeaux mixture (other than as a fungicide) upon plants. Prominent 

 among these investigators were Zimmerman (1893, P- Z'^7)y Rumm 

 (1894, p. 445), Gallowa}^ (1895), Frank and Krliger (1894, p. 8), and 

 Aderhold (1893). Aderhold concluded that the increase in growth was 

 due to the lime of the bordeaux mixture being absorbed by the roots. 

 Frank and Kruger held that it acted as a stimulus, as did also Rumm, 

 while Zimmerman opposed this view maintaining that the solutions 

 were absorbed directly by the leaves. 



It has recently been observed that the application of ether vapour to 

 foliage leaves stimulates the plant to a more rapid development, and 

 horticulturists have taken advantage of this to force plants for the 

 market (Fisher, 1900, p. 283-284). This shows rather clearly that 

 chemical substances applied to the leaves of plants may be made to 

 promote growth as well as to injure the plants. In the work of Lawes 

 and Gilbert (1883), it is shown that certain substances in the air, 

 especially in the neighbourhood of towns and cities, at times, affect 

 injuriously the foliage of plants. Some investigations with this end in 

 view, were recently carried on by Wieler and Hartleb (1900, p. 188) 

 with a view to learn the effects of HCl upon .the assimilation of 

 plants. 



The question of the destruction of weeds by poisonous chemical 



