igoo-i.] Effects of Water on Foliage Leaves. 315 



It was found that the solutions appHed to the lower side were 

 absorbed more quickly. 



These experiments show that the leaves of this plant are more 

 sensitive to these solutions when they are applied to the lower surface. 



When drops of these solutions were placed upon leaves of 

 Bouvardia, there were distinct spots " scorched " upon the leaves, but 

 when a filter paper was saturated with some of the solution and folded 

 flat upon the leaf, upper and lower side being covered, there was no 

 visible effect. This seemed very peculiar, more especially as the paper 

 was saturated three times upon three successive days, enough of the 

 solution being applied to kill several leaves if placed upon them in 

 drops. This may have been due to the fact that the filter paper* held 

 the solution mechanically in its tissue by capillary action, and as the 

 water evaporated, the salt was retained in the paper ; little, if any, 

 could have entered the leaf 



When the solution of CuSOi, and solutions of those substances, 

 which produced dark* green rings at the margins of the drops, were 

 applied in sufficiently low concentration to cause no "scorching" of 

 the leaf, but yet strong enough to bring about after some time this 

 darkening of the green colour (see also Griffon, An. Sc. Nat. 8, 1-2, 

 1899), the action was probably in the nature of a stimulus to growth, 

 and produced a better development of chlorophyll and of protoplasm in 

 the region where the tissue appeared dark to the naked eye. (See 

 Fig. 12). The explanation of this is given in the chapter on "Tobacco 

 Leaf Spot." 



The yellow spots and marginal stains noticed by Smith upon the 

 leaves of plants (1872), were due to the poisonous substances held in 

 solution by water clinging to the leaf, either in the form of drops, or 

 held by capillary action on the edge of the leaf. The poisonous 

 substances came, as Smith showed, in the form of fumes, from the 

 neighbouring chemical works. How exceedingly sensitive plants are 

 to these noxious vapours and fumes, is shown in the following 

 statement of Smith : — " When the air has so much acid that two to 

 three grains are found in a gallon of rain water, or forty pints in a 

 million, there is no hope for vegetation in a climate such as we have 

 in the northern part of the country." 



In discussing the question of the application of solutions to leaves 



^ This is in accordance with the common method of purifying^ distilled water from compounds ot 

 copper, etc., by placing pure filter paper in the water. 



