THE ART OF REARING 
28U 
harsh, and tough, which is given to silk-worms 
in . some of the warm climates of Europe, in Spain, 
in Sicily, in Calabria, and in some parts of Greece, 
fyc., produces abundant silk, the thread of 
which is very strong, but coarse. 
The white mulberry leaf of the tree planted 
in high lands, exposed to cold dry winds, and in 
light soil, produces generally a large quantity of 
strong silk, of the purest and finest quality. 
The leaf of the same tree, planted in damp si- 
tuations, in low grounds, and in a stiff soil, pro- 
duces less silk, and of a quality less pure and fine. 
These are the most observable differences ; there 
are others relative to the topographical situations 
of the establishments. 
The less nutritive substance the leaf contains, 
the more leaves must the silk-worm consume to 
complete its developement. 
The result must therefore be, that the silk-worm 
which consumes a large quantity of leaves that 
are not nutritive, must be more fatigued and more 
liable to disease, than the silk-worm that eats a 
smaller proportion of more nutritive leaves. 
The same may be said of those leaves which, 4 
containing a sufficiency of nutritive matter, con- 
tain little resinous substance ; in that case the 
insects would thrive and grow, but probably 
would not produce either a thick or strong co- 
coon, proportionate to the weight of the silk- 
