Tuesday 20 December 2016

Willow twigs and aphid eggs


Here are some views of Salix viminalis twigs and buds, showing the greyish hairs on the twigs and buds. The buds have just one outer bud-scale, and are flattened against the twig, as is characteristic of the genus.


In this closer view you can see the placement of the lenticels on the "shoulders" of the buds - perhaps a very useful place for them to be metabolically? It is also interesting to see the "lipped" appearance of the buds, which may, or may not, be somewhat characteristic of the species - they may have dried out a bit of course. And, is it genuinely S. viminalis?

The other thing is the three small horns on the leaf scar - the two outer ones are smaller and "sharper" and sometimes appear to have a circular scab just to the outside of the horn, and I am finding it difficult to interpret this pattern. One possibility is that the circular scab results from the abscission of a stipule - as suggested on this webpage. The horns would therefore perhaps be "now blocked off" veins? If so the two outer ancillary ones may join with the central main one to form the midrib of the leaf, but perhaps branching off again in the lower quarter or third of the blade. Or could they be for stipule venation?


Several of the twigs had aphid eggs on them, quite glossy black by now.


Here are two more eggs


This is a twig from one of the yellow-orange Crack-Willows, Salix fragilis, on the Southern side of the Ocean lake. The stipule scar is very obvious and the bud itself is quite solid-looking, almost thorn-like at this angle. So many of them seem quite sharply colour-banded.


This is another twig of Crack Willow, this time with one partly diseased bud, a not uncommon sight in my limited experience.


This is a Dogwood twig, showing the spiky opposite unscaled buds that look to me like "witch's fingers"



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