is a very common thing for drains to operate perfectly for indefinite
periods, where they run through forests and orchards for long distances.
They, however, who lay drains near to willows and ashes, and the like
cold-water drinkers, must do it at the peril of which they are warned.

Laying the tiles deep and with collars will afford the best security
from all danger of this kind.

Thos. Gisborne, Esq., in a note to the edition of his Essay on Drainage
published in 1852, says:

My own experience as to roots, in connection with deep pipe
draining, is as follows:--I have never known roots to obstruct a
pipe through which there was not a perennial stream. The flow of
water in Summer and early Autumn appears to furnish the attraction.
I have never discovered that the roots of any esculent vegetable
have obstructed a pipe. The trees which, by my own personal
observation, I have found to be most dangerous, have been red
willow, black Italian poplar, alder, ash, and broad-leaved elm. I
have many alders in close contiguity with important drains; and,
though I have never convicted one, I can not doubt that they are
dangerous. Oak, and black and white thorns, I have not detected,
nor do I suspect them. The guilty trees have, in every instance,
been young and free growing; I have never convicted an adult.

Mangold-wurzel, it is said by several writers, will sometimes grow down
into tile drains, even to the depth of four feet, and entirely obstruct
them; but those are cases of very rare occurrence. In thousands of
instances, mangolds have been cultivated on drained land, even where
tiles were but 2-1/2 feet deep, without causing any obstruction of the
drains. Any reader who is curious in such matters, may find in the
appendix to the 10th Vol. of the Journal of the Royal Ag. Soc., a
singular instance of obstruction of drains by the roots of the mangold,
as well as instances of obstructions by the roots of trees.

_Obstruction by Per-oxide of Iron._ In the author's barn-cellar is a
watering place, supplied by a half-inch lead pipe, from a spring some
eight rods distant. This pipe several times in a year, sometimes once a
week, in cold weather, is entirely stopped. The stream of water is never
much larger than a lead pencil. We usually start it with a sort of
syringe, by forcing into the outlet a quantity of water. It then runs
very thick, and of the color of iron ru