1897] NORMAL AND DISEASED ORGANS OF ABIES BALSAMEA 3Ir 
Il. GENERAL CHARACTERS OF THE WITCH BROOM. 
4. elatinum Alb. & Schw. usually attacks the younger lateral 
branches of A. dalsamea (L.) Mill. which take the infection either 
in the young shoots, or in the wounded bark of older ones. 
Branches over five years old seldom take the infection, differing 
in this respect from A. pectinata, which often has large swellings 
on the older branches and on the main trunk, due to this 
disease. It often happens that the terminal shoot becomes 
diseased, in which case the whole tree soon dies from insuffi- 
cient light, not being able to increase in height fast enough to 
keep out of the shade of surrounding trees. 
The irritation due to the fungus mycelium causes an increased 
growth of the bark and wood at the first point of infection, pro- 
ducing a so-called “boil” or tumor on the diseased branch. 
This tumor is always present and increases in diameter with the 
increase in age of the witch broom. The diseased annual shoot 
is shorter, but has a greater diameter than the normal. 
Owing to the development of a greater number of the latent 
and lateral buds of the affected branches, the number of the 
diseased branches above the normal is greatly increased. In 
this way a sort of broom is formed. The leaves of the diseased 
branches spread on all sides like the leaves of the erect terminal 
shoots. This is partly due to the fact that the terminal as well 
as the diseased branches are all negatively geotropic, unlike the 
normal lateral branches which are diageotropic. On account 
of the absence of chlorophyll the diseased leaves have a yel- 
lowish color. The leaves of the diseased branches are about 
one half as long as the normal leaves of the lateral branches, but 
they are usually of the same length as the leaves of the normal 
terminal shoots. The normal leaves of the lateral branches 
are arranged nearly in one horizontal plane, not because the 
7 phyllotaxis is altered, but because the leaves are twisted more 
Or less at the base, just above the pulvinus. It is easy, therefore, 
betes 
=e 
distinguish between the normal and diseased branches, the 
rmal ones always having this apparent distichous leaf arrange- 
