454 
Journal of Agricultural Research 
Vol. XXVI, No. 10 
(fig. 2, A and B.). Under certain conditions chlamydospores are formed 
from the cells of the macroconidia (fig. 2, C.). 
Cover glass cultures, made by using transfers from culture No. 45, 
when examined under the microscope, showed chlamydospores of the 
fungus budding and .finally germinating (fig. 2, E.)* Chlamydospores 
taken from a reddish crustlike mass inside a hollow knot, when observed 
in hanging drop cultures, showed a similar budding process, resulting in 
the formation of large numbers of these spores (fig. 2, F.). Hyaline, 
one-celled and two-celled microconidia were also present and their 
germination noted (fig. 2, I.). The older mycelium produced in all 
these cases showed yellowish to reddish cell contents. 
The fungus appears to develop rapidly under very moist conditions. 
This rapid growth was observed in the artificial inoculation of blocks of 
fresh sapwood placed in humidity chambers. 
Cultural tests using pieces of red-stained boxelder kept in the air-dry 
condition of a room for a period of one and a half years show that the 
fungus is capable of reviving at the end of this period. Cover glass 
cultures made by placing microtome sections of the infected wood on a 
thin layer of agar under a cover glass showed that the new hyphae at the 
time of revival may originate from old hyphae or from chlamydospores 
formed in the tissues. Eidam states: 
In culture in the moist chamber the mycelium grows out from the wood and the 
brown hyphae put forth young colorless filamentous branches which phosphoresce 
very beautifully and distinctly so that thereby the whole outline of the piece of 
wood showed distinctly. 
PATHOGENICITY 
Numerous isolations of Fusarium negundi Sherb. in pure cultures 
obtained from fragments of the stained wood prove the constant asso¬ 
ciation of this fungus with this particular disease, which is characterized 
by a reddish discoloration. Comparisons of the hyphae and spores 
produced in pure cultures with those found in and upon the red-stained 
wood furnish additional evidence. Conidia (fig. 2, I.) and chlamydo¬ 
spores (fig. 2, F.) resembling closely those produced in pure cultures 
were found on infected trees in the debris scraped from hollow knots 
and from cavities in the bark produced by species of sapsuckers. 
Poured plate dilution cultures made from this spore mass developed 
colonies of a Fusarium which colored the agar a bright red and which 
were identified as Fusarium negundi Sherb. Information gathered in 
connection with sapsucker injury, leads to the opinion that the fungus 
is either weakly parasitic or develops on the injured tissues and produces 
discoloration of the surrounding sapwood tissues by diffusion of the 
colored matter which is in solution. By far the greater number of 
infections so far found in the sapwood of the living tree have their origin 
in the wounds produced by sapsuckers. (PI. 2.) 
The red stain was produced artificially in the laboratory on boxelder 
wood by inoculation with the fungus from pure cultures obtained from 
the red-stained wood. Difficulty was experienced in attaining positive 
results when heartwood of boxelder was used after sterilization by auto¬ 
claving for a period of 45 minutes at 15 pounds pressure. Better results 
were gained by using fresh sapwood blocks, surface sterilized by washing 
in mercuric chlorid and distilled water. Table I gives the results of 
these experiments. The fungus reisolated from a stained spot on one 
of the blocks was found to be identical with Fusarium negundi. 
