Perhaps we need to update Fig. 618 in the keys. Is the lumen inside the gall
continuous? I had assumed that it was but, I admit, I haven't dissected the
galls! So, Malcolm, could you send me some specimens to check? Address: 2
Victoria Road, Sheffield S10 2DL. Fig. 618 has 2 and a bit twists, which fits
OK with the couplet, but I agree that perhaps we could phrase the description
better.
Thanks,
Margaret

Quoting Malcolm Storey <malcolm.storey@...>:

> Am just looking at a collection of Pemphigus spyrothecae Spiral Galls on
> Lombardy Poplar from Newbury, Berks. They all have a single twist - ie only
> one crack opens up when you gently uncurl very slightly. In the AIDGAP galls
> book (Redfern et al) it is described as having 2-3 twists. Think the concept
> of "twists" is misleading. If it had 0 twists it would still have a single
> thickened layer, 1 twist would give 2 layers, so 2 twists gives 3 layers.
> Fig 618 shows a specimen with 2 twists (ie 3 layers - or maybe just one
> twist - the original line of the petiole often gives a groove which looks
> like a join - the drawn section [incorrectly] shows the tissues continuous -
> ie no twists). Suspect the drawing might be more often interpreted as 3
> twists. But am not sure how better to phrase it! Perhaps use the no of
> cracks that open up when you uncurl it slightly.
>
>
>
> Maybe this pedantry is a long term after-effect of a PhD project that
> involved counting the no of whorls on several hundred snail shells. ;o)
>
> HTH
>
> Malcolm
>
> www.bioimages.org.uk
>
>
>
>