Disease Clues?

Two hemlock branch tips, each two inches long, one from a diseased hemlock at Seward Park, the other from a healthy mature tree at Schmitz Preserve in West Seattle.  The Seward tree has lots of “brooms”, but one branch with needles hung down low enough to reach. (Since hemlocks die from the bottom up, their needles can be hard to reach.)  The Schmitz hemlock was healthy top to bottom, no brooms, all the branches in fine health, even as low as two feet from the ground.  I believe that both branch tips have new growth in the apical half, with last year’s growth towards the base, somewhat visible below in lighter vs darker shades of green.

We stripped the needles off both branch tips as seen above, then traversed each with a hand-held microscope, creating two clumsy videos shown below. First the healthy branch, then the apparently diseased one – which exhibits a lot of cryptic black substance – which may be adventitious, opportunistic or unrelated to die-off. Or it may be a clue about cause. An additional ten samples in each of these two observation classes may be found on youtube, the apparently healthy cases here, the affected cases here. We make no claim about cause and effect here, but do suggest that further study of this phenotype may be fruitful.