igoo-i.] Effects of Water on Foliage Leaves. 257 



and in dew, are resorbed by leaves under certain conditions, it seems 

 probable that water may be absorbed. This last mentioned point will 

 be discussed in detail in the following chapter. 



IV. — Incrustations, Guttation Drops, Dew. 



Certain plants, belonging to the orders Saxifragacece and Phim- 

 baginacecs, are frequently, when under natural conditions, found with 

 incrustations upon the leaves, and the chief object of this chapter is to 

 make clear, if possible, the cause and the function of these peculiar 

 deposits of lime and other substances upon foliage leaves. 



The chemical composition of this deposit has been examined by 

 several botanists, notably Treviranus, Mohl (1861, p. 227) and Volkens 

 (1884), and they all agree that the inorganic part of the deposit is 

 composed almost wholly of CaCO;,. They found also a certain amount 

 of organic matter associated with it, but this they did not analyze in 

 detail. 



To see if this deposit could be produced artificially, dew-drops were 

 taken in early morning from time to time, from leaves of the following 

 plants, — Trapseolum, Lilac, grass, Mentha, and Polygonum, and placed 

 upon clean cover-glasses. The cover-glass being now kept free from 

 dust, the dew was allowed to evaporate. When the drop had evaporated, 

 a deposit of a whitish crystalline substance remained, showing clearly 

 that the dew-drop had held in solution some salts. Upon carefully 

 heating the cover, and then examining with a lens or microscope, one 

 could see that a certain amount of charred substance had been produced 

 by the heating. This charring indicates the presence of some organic 

 substance. The inorganic portion is soluble in dilute HCl, with 

 liberation of CO,, showing that a carbonate is present. The quantities 

 were too small to permit of a further test for the base or bases in 

 solution, but as considerable of this substance is re-dissolved in distilled 

 water, there arises the suggestion that it is not all CaCOg, but very 

 probably largely potassium carbonate with potassium oxalate. 



Since the dew is, in part at least, formed by the condensation of 

 aqueous vapour of the atmosphere, the question arises as to the source of 

 the salts which were deposited when the drops were evaporated. Did 

 they come from the tissue of the leaf or were they derived from the 

 atmosphere ? To answer this question a series of experiments was 



