CROWN-ROT OF FRUIT TREES: HISTOLOGICAL STUDIES 505 
the different buds and nodes on the same branch varied greatly in 
their susceptibiHty to injury; some remaining normal while others 
were entirely killed. 
Miiller-Diemits and Stormer-Halle^^ found that fruit trees are most 
subject to bark diseases at the age when they first become profitable. 
The bark at the crown, crotches, and various other places on trunks 
and branches, according to these authors, dies; fungi and bacteria 
enter the wounds and induce further injury and decay. The wood 
becomes discolored, and the branch or tree involved dies. 
As an illustration of the especial susceptibility of trees to bark 
injuries and the resulting diseases, during certain stages in their life 
history, especial attention may be called to the bark-roughening 
discussed above as well as to this paper by Miiller-Diemitz and 
Stormer-Halle. The older literature of forestry contains many items 
of interest in this connection. Graebner,^*^ for example, described a 
case of this kind, and in the writings of Hartig, Nordlinger, Hess, and 
others, are to be found many further instances. Graebner found that 
a high percentage of trees in a spruce forest had sustained bark injury 
on their trunks. Very many of them died of crown-rot. The trees 
had apparently been from 34 to 57 years old at the time the injuries 
occurred. In an adjoining spruce forest, where the trees were under 
20 years of age, no bark injury could be found. It appears from 
various published statements that spruce trees in a forest stand usually 
become rough-barked between the ages of 30 and 40, depending upon 
the rate of growth and thickness of stand. 
Conclusions 
The histological study here briefly reported, in connection with 
my two former papers, throws enough light on the earlier stages of 
crown-rot to permit more definite and general statements regarding 
its development. It is shown that this and some related bark diseases 
are not due primarily to the organisms usually found in such affected 
bark in summer, but to injuries arising when adverse environmental 
conditions overtake trees having immature bark in certain regions. 
The rotting of the dead or dying bark is due chiefly to fungi which in 
^^Miiller-Diemitz, J., und Stormer-Halle, K., Das Obsthaumsterben, Deutsch. 
Obstbauzeit. 56: 81. 1910. 
Graebner, P., Beitrage zur Kenntnis nichtparasitarer Pflanzenkrankheiten 
an forstlichen Gewachsen, Zeit. Forst. Jagdwesen. 38: 705. 1906. 
