1900-1.] Effects of Watf:r on Foliage Leaves. 311 



overcome by the attraction between it and the gla.ss, and of ^gravitation, 

 it assumes the form of a flattened spheroid, something like the form 

 shown in the diagram. The curves BFA and DGE being sharper than 

 any other curves on the surface of the drop, there will be a greater 

 surface exposure to the air in proportion to the mass of liquid in the 

 immediate vicinity, and consequently a greater evaporation and 

 condensation of solution. There will clearly be less evaporation from 

 the surface AC than from the surface .AOC ; and if AOC be a similar 

 curve to a part of BFA, there would be less evaporation from AC than 

 from the part referred to of BFA. Now it follows, as diffusion through 

 liquids is very slow, that the first crystals will form at B and D. These 

 crystals are now no longer floating, but take up a fixed position — from 

 their weight — upon the glass, and remain there. As evaporation 

 proceeds, the distance from C to the plate becomes less and less, while 

 the distance BD along the plate remains almost constant ; BCD 

 becomes BMD and BND. This is due to the fact that the crystal in 

 growing attracts other particles towards it to build it up, and as it 

 cannot now move, the particles move to it ; and also because the 

 substance of the crystal, having a strong affinity for water — otherwise it 

 would not dissolve readily — attracts water towards it, because of a 

 physical affinity now called capillarity, aird which some term surface 

 tension. If a drop, half evaporated, be placed under the microscope 

 this may be easily observed, and it will then be noticed that the margin 

 of the area of contact between the drop and the glass is only very 

 roughly the circumfefence of a circle, because the crystals first formed, 

 (not being formed all at the same time), will be distributed irregularly^ 

 the first farthest from the centre. The place of the first crystals laid 

 down will determine the position of the ring of salt found after 

 evaporation has been completed (represented by C and C" in diagram). 

 The prominence of the ring will depend upon several things, — affinity of 

 the substance for the solvent, crystal-forming power, and the diffusing 

 power of the substance in solution, etc., which it is not necessary to 

 discuss here. 



Though the solution was applied to the lower surface of the leaf, 

 there was an effect more plainly visible upon the upper surface, showing 

 that the solutions had acted especially on the cell contents and upon the 

 chlorophyll granules. The substances were conveyed through the 

 spongy tissue in the lower portion, to the palisade tissue where the 

 chlorophyll is most abundant. The ring, in several instances, was well 

 marked upon the upper, as well as upon the lower surface. Those 

 substances remaining moist, did so because of their strong hygroscopic 

 properties. 



