Ceratostomella ulmi, de geslachtelijke vorm vangraphium ulmi schwarz

Summary

The speciesGraphium ulmi Schwarz consists of two sexually different groups (+ and—strains). By growing both sexes together on sterilized elm twigs perithecia can be produced that belong to the genusCeratostomella. A description of thisCeratostomella (Ceratostomella ulmi follows.)

Perithecia black, round, normally 105–135μ (mean 123μ) in diameter, rarely bare, mostly provided with a few scattered hairs. Necks often slightly curved, 265–380μ long, breadth at the base 24–38μ, at the top 10–16μ. The hyphae the neck consists of diverge at the top and form a crown of cilia. Cilia about 24 in number, septate, sometimes swollen at the top, very variable in length, usually 25–60μ long. Asci imbedded in a slimy mass. Ripe asci disintegrate in water, which prevents taking their exact size and determining the number of spores per ascus with certainty. Probably an ascus contains 8 spores. Ascospores slightly curved, shaped like the parts of an orange, measuring 4,5–6×1,5μ.

Perithecia not yet found in nature. They can be produced by combining +en—strains ofGraphium ulmi Schwarz.