In message , Jeff Layman
writes
On 13/06/2011 12:43, Stewart Robert Hinsley wrote:
On Saturday I saw a white-flowered shrub on the far bank of a canal.

http://www.stewart.hinsley.me.uk/Images/Shrub05a.jpg
http://www.stewart.hinsley.me.uk/Images/Shrub05b.jpg
http://www.stewart.hinsley.me.uk/Images/Shrub06a.jpg

I interpret it as having opposite foliage, which eliminates all the
various rosaceous shrubs. The venation pattern of the leaves is wrong
for Philadelphus, or at least the common forms (and more obviously the
flowers have the wrong number of petals). I don't think it's Deutzia
either.

At this point I run out of ideas. Any offers?

A decent pair of waders?

Thumb a lift on a narrow boat?

I'm puzzled by your comment that it can't be rosaceous as it has
opposite foliage. According to my RHS Dictionary of Gardening,
Philadelphus has "Leaves usually deciduous, opposite, simple". In any
case, are you sure that the leaves are not compound? Some in
Shrub06a.jpg about half-way down on the extreme right appear to be
opposite leaves, but could be a compound leaf. Agree with you about
the number of petals, though.

Philadelphus is not rosaceous (it's a member of Hydrangeaceae). I had
eliminated rosaceous plants (principally Pyrinae) on the grounds of
opposite foliage; I then proceeded to eliminate another alternative -
Philadelphus.

I take your point about the possibility of a compound leaf, which in
theory would bring Rosaceae back into the reckoning. It's not Sorbus;
and it didn't shout out Rosa either - any other possibilities?

But I see that other people are convinced that it's a rose, and now I
know what I'm looking for I can see the thorns, and stipules of compound
leaves. Rosa multiflora is the most likely - it does occasionally turn
up in wildish contexts.
--
Stewart Robert Hinsley