et [Vor. 1 
256 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
here and there some of them are dissolved, giving rise to small 
separated cell groups. Entire dissolution rarely takes place 
(this was also found to be true for diseased catalpa wood ((5) 
pl.52)). With the removal of the secondary thickening, the 
resulting decayed wood has a skeletonized appearance. It 
has all of the elements, but these are very thin-walled. Тһе 
fine medullary-ray cells are destroyed here and there, producing 
radial, isolated masses, but more frequently the decayed mass 
hangs together firmly. Тһе dissolution of the layers of secon- 
dary thickening goes forward very evenly, bringing about the 
sharp dividing line between sound and decayed wood already 
referred to. 
Тһе only difference between the catalpa and Шас diseases is 
that in the catalpa the entire wood mass is skeletonized, whereas 
in the Шас hard areas of undestroyed wood fibers are left here 
and there, surrounded by decayed wood (pl. 9 figs. 1, 2). "These 
masses are either entire rings (pl. 9 fig. 1) or irregular areas 
lying detached within the decayed parts, and represent portions 
of the heart-wood which for some reason have temporarily es- 
caped total destruction; the wood fibers are filled with the yellow- 
brown substance, but do not otherwise differ from normal wood 
fibers. As the disease progresses, however, they are finally 
destroyed. This was made evident by the fact that in the 
upper parts of diseased trunks these immune areas were always 
found coexistent with the early stages of the disease, while 
lower down in the trunks, where the advanced stages of decay 
had been reached, they were practically absent. The temporary 
immunity may be due to the presence of more resistant groups 
of wood fibers, possibly also to a high concentration of decom- 
position products. 
'The development of the fungous mycelium from the center of 
the trunk out toward the bark differs radically from that of any 
other disease known to the writer. In most trees the destruc- 
tion of wood by a fungus growing in the dead heart-wood is 
confined to the latter,—further growth ceasing as soon as the 
mycelium reaches the sap ring. Ав has been suggested by 
Münch (4), this is probably due to the fact that most mycelia 
of wood-destroying fungi require a balance between the amounts 
of oxygen and water contained in the wood fiber. Any undue 
