30 TREES OF MASSACHUSETTS. 
should take place, the woods must contain trees of various kinds 
sufficient to supply the whole surface with seed. When this is 
the case, a wood of one kind will usually be found full of little 
trees of other kinds. ‘‘Upon clearing off the old growth, the 
undergrowth, which has been kept from the sun, shoots up 
with astonishing rapidity.” * That portion of it which is most 
unlike the previous growth, finds plentiful nutriment, while the 
proper food of the previous forest has been exhausted, and the 
woods naturally change their aspect. 
The forests, as has been stated, form or improve a soil. ‘This 
they do by their annual deposit of leaves, and by rendering the 
ground accessible to air, by the action of their roots. Both 
operations are essential, and aid each other. If the leaves were 
not deposited, the surface of the ground would speedily become 
dry and hard, and the radicles which had previously pervaded 
it, would be exposed to cold in winter, and to heat and drought 
in summer. ‘The covering of leaves protects against all. By 
them the superficial portions are kept moist and soft, and per- 
meable by the delicate radicles, and these are protected, while 
they are made readily accessible to moisture from rain charged 
with carbonic acid, and to air and atempered warmth. The 
covering of leaves thus secures all those circumstances which 
are most favorable to vegetable growth. It is, therefore, justly 
enumerated, by some of my correspondents, among the things 
most unfavorable to the growth of trees, to gather the leaves 
together, as is frequently done, either to burn them or to add 
them to the compost heap. This is bad economy. It is double 
robbery. It is taking from the forest what belongs to it, and is 
almost essential to it, and it is spreading, with loss of time, upon 
the present cornfield, what, left undisturbed, is at once a store- 
house and laboratory of manure for the future comfield, on 
which it is already spread and spreading itself. 
The other circumstances enumerated as particularly unfavor- 
able to the growth of trees, are browsing, pruning, a thin soil, 
exposure to sea breezes, to high winds, and to frosts. 
* Mr. A. Bacon, of Natick. 
