CRACK, OR RED-WOOD WILLOW. 



155 



factorily ascertained, and it is still a matter of conjecture 

 whether it is to be attributed to the soil, or to an inherent 

 taint in the slips or cuttings by which it is usually propa- 

 gated. 



When first cut the sap wood of the Crack Willow is 

 white, the heart pale red ; upon exposure to the air, and 

 when seasoned, both become of a fine salmon colour. The 

 bark is bitter and contains a large proportion of tannin, 

 as well as a bitter principle termed salacine, akin in its 

 properties to quinine. The roots afford a purple red dye, 

 and are still used in Sweden and in France to colour the 

 Paschal or Easter eggs, a use to which they were also 

 formerly applied in Scotland. 



The larvse of several nocturnal lepidoptera feed upon 

 the leaves of this as well as other willows ; among them 

 we have found those of Cerura vinula, Notodonta ziczac, 

 and Smerinthus populi. 



