Birch, River
A 10' high river birch tree planted several years ago has shown disease symptoms. The leaves look a bit ragged, and about 20% of its leaves turned yellow and were shed a few weeks ago. A year or two ago it had even more severe problems and almost died. A fungicide spray helped revive it. The following set of leaf pictures were taken in early August, using a 400 power digital microscope.
While the leaftop was mostly clear, there were numerous elongated white objects that appeared to be erupting from the surface, as shown above. It appears as if these objects are forcing their way out, splitting the leaf surface in the process.
The leaf tops were peppered with what looked like yellow egg yolks. Usually they were clustered near a leaf vein and very often they had a waxy white substance around them, as shown above, giving them the appearance of a fried egg.
The leaf bottom was similar in that these egg yolk objects were far more common, as shown above.
The next set of pictures shows microscopic views of the bottom of the leaf. They are only a little more useful than the top set of pictures.
But even more information was contained within a cross-section of a 1/8 inch twig from the tree. These three pictures show that the green growth (cortex) and nourishment area (phloem) directly under the bark is riddled with white waxy growths (black arrows).

Note the blue 50μm scale bars in all the pictures. The purple arrow points to the white plastic vise grip used to hold the sample.

It seems likely that these white, waxy, cankerous growth areas are the probable cause of this tree's problems.

Some parts of the leaf bottom also had lots of associated hair-like structures, as the above picture shows.
The leaf vein accentuated this pattern, having far more "hair" on it, as well as a concentration of light orange globules. Several of the white spores seen on other plants were also present.
The leaf stem was even more colorful, containing the same light-orange globules, light-yellow globules, white waxy objects, and translucent hairs.

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