48 BULLETIN OF THE BUSSEY INSTITUTION. 
the most part of leaves that have not only fallen, but have been leached 
by rains, are, of course, much less valuable than fresh leaves, such as 
were just mentioned. They may be classed as somewhat inferior to 
straw. It is to be remembered, in this connection, that when a plant 
ripens, or makes ready for hibernation, a good part of the valuable 
constituents of its leaves pass out from the leaves into the fruit or the 
stem or the root of the plant, there to be stored up for future use. It 
appears from the table in Volume I. that dead beeclt-leaves collected 
in autumn may contain from 0.1 to nearly 0.5% of potash, and from 
0.06 to 0.35% of phosphoric acid. Rissmiiller (‘ Versuchs-Stationen,” 
1874, 17. 25) found 1.25% of nitrogen in beech-leaves, plucked Nov. 
18 and dried at 100°, which is perhaps more than could be fairly 
expected on the average from leaves that had actually fallen. Stoeck- 
hardt (in his “ Feldpredigten,” 1856, 2. 111) puts the amount of nitro- 
gen in fallen beech-leaves at 0.8%. 
It should be distinctly understood that there is nothing, in the fore- 
going statement, which detracts from the merit of tan or sawdust or 
‘leached dye-woods, considered merely as materials for mulching. The 
efficacy of a mulch, viewed as such, depends upon its mechanical 
texture or condition, and not upon its chemical composition ; and long 
experience has taught that the substances now in question may often 
be used, very advantageously, as mulches. Indeed, in many of the 
accounts that have from time to time been published of the beneficial 
action of tan composts, or the like, there are plain grounds for suspect- 
ing that the tan or sawdust really did good service as a mulch, and 
that the benefit supposed by the experimenters to have been derived 
from fertilizing ingredients in the tan was really due to another cause. 
The utility of spent tan as a mulch for fruit-trees has long been 
known. Many writers have insisted that the tan keeps the ground 
damp and “loose” and “open,” as the terms are, or “in a good state 
of fermentation,” to translate somewhat freely the German term 
Giihre ; and it has been thought by many that fresh tan tends to pre- 
vent the approach of various insects that might harm the trees or 
fruit. As Professor Johnson has well said, “ Fresh sawdust in light 
thirsty soils tends to increase the water-holding capacity. In sticky 
clays it lightens the texture; and, on soil that forms a hard crust after 
rain, it prevents, like any other mulch, such puddling and baking of 
the surface.” 
