26 MISSOURI BOTANICAL GARDEN. 
medullary rays when invaded by the mycelium are rapidly 
destroyed. They can be recognized as brown lines extend- 
ing outward into the sound wood (Plate 3,m). The large 
conspicuous vessels are completely filled with brown hyphae, 
which have riddled the walls of the thylloses, but have not 
entirely absorbed them. Passing toward the more decayed 
parts one finds the small woodcells attacked, here and 
there, so that small groups lie embedded in a felt of hyphae. 
Even these gradually disappear (see the middle of Plate 3) 
and one has only remnants of the large ducts. The walls 
of the latter appear to be the most resistant parts of the 
wood, and even in completely decayed wood, such as is 
represented at the top of Plate 3, one can always recognize 
the place of the former ducts by separate pieces which the 
fungus has not been able to destroy. The walls of the 
thylloses are similarly resistant, and can be recognized, to- 
gether with the walls of the ducts (Plate 3). Both stain 
deep red with phloroglucin and hydrochloric acid, showing 
that they have suffered no change whatever. 
The manner in which the walls of the woodcells are 
dissolved varies in different parts of the trunk. The first 
change noticeable in both medullary ray cells and the wood- 
cells is the disappearance of the yellow-brown coloring 
matter. This is followed by the solution of the middle 
lamellae of the medullary ray cells and the destruction of 
the lignin elements of the latter, leaving the white cellulose 
fibres free from one another. These in turn soon disappear 
completely, and their place is taken by masses of brown 
hyphae. Similar changes take place in the wood here and 
there, resulting at first in the conversion of large masses of 
wood fibres to cellulose; these in turn are completely dis- 
integrated. In the more common form of destruction the 
woodcells are not converted into cellulose. The hyphae 
penetrate the woodcells in all directions, riddling the walls 
with larger and smaller holes, so that they gradually break 
into small isolated pieces, which can be observed embedded 
