204 Botanical Society of Edinburgh. 
roots had penetrated the drains in different localities, were :—elm, 
poplar, willow and ash, Polygonum Bistorta, Equisetum, and Tussilago 
Farfara. ‘The Bistort had been very troublesome in the Carse of 
Gowrie. Mr. Gorrie had found the roots of an alder penetrating 
into an old mine full of water, and developed there in a remarkable 
manner. 
Dr. Neill stated that twenty years ago Mr. Riddoch of Falkirk 
had transmitted to him a specimen of the root of Senecio Jacobea 
that had entered a drain by a very small orifice, but afterwards ex- 
tended itself, completely filling the drain for about 20 feet. 
Mr. Wyville Thomson referred to an instance which had come 
under his observation in Ayrshire, in which drains were completely 
obstructed at a place where they passed through a larch plantation, 
the roots of the larches having filled them up. 
Sir John S. Forbes, in a letter addressed to Professor Balfour, gave 
some interesting particulars as te the water-pipes which supply the 
village of New Pitsligo, Aberdeenshire. Part of these tile- -pipes, 3 
inches bore, were laid about forty years ago, overlapping 24 inches, 
packed in clay throughout their whole length, and the ‘oints filled 
with milled clay. The pipes are in general. placed 3 feet deep; but 
in some instances they approach nearer the surface owing to the 
levels, and at these points roots have entered. The roots proceed 
from plants outside and never adhere to the tile. They run along 
the inside for 6 or 8 yards, and then become matted together so as 
to fill the pipes completely. The plants which have been observed 
to send their roots into the pipes are species of Rumex and Carduus, 
&c. The pipes require to be cleaned at least once in the season, 
which is done by a long wire with a screw at the end, which is 
twisted among the roots so as to break them up, and allow the 
loosened matter to pass out at the lowest level. Sir John sent a 
specimen of the root of a gooseberry bush which had entered the 
pipes where they passed through a garden. 
Dr. Fleming suggested the importance of ascertaining the probable 
structural changes which enabled the roots of these plants to derive 
nourishment directly from running water. 
Dr. Balfour exhibited specimens of a peculiarly knotted stem of 
an elm from Prestonhall. ‘The leading stem had been broken off, and 
one of the side branches rising from a remarkably knotted base had 
become erect, giving the tree a peculiar aspect. All the branches of 
this new leader were covered with knots, while the other branches 
were free from them. The peculiarity v was continued in plants raised 
from slips taken off the branch. 
Dr. Balfour also noticed the occurrence in Prestonhall grounds of 
a mountain ash, from which a large limb had been broken, splitting 
the tree so as to expose its centre, which is now covered with roots, 
sent down from the branches above. 
Dr. Balfour exhibited specimens of sycamore roots, taken by Mr. 
Gorrie from very stony ground, which had become flattened and hol- 
lowed so as to embrace large stones at different points. The roots, 
when removed, carried the stones with them, and in some instances 
