28 BULLETIN 360, U. S. DEPARTMENT OF AGRICULTURE. 
It is a well-known fact that wounds heal quickly in young or in 
strongly growing trees, principally due to the protection afforded by 
an abundant flow of resin. It may be assumed that trees having their 
hfe functions brought to a low ebb by excessive mistletoe infections, 
with resulting decrease in annual increment, will not be able to heal 
or protect their wounds as quickly as normal trees; hence, are more 
lable to infection. This may be one of the reasons why so many 
open burls are formed on infected larches. These open burls are 
seldom, if ever, healed, although the parasite in its tissues has long 
since died. There is a shght increase in the number of resin passages 
~in early burl formations, but this is entirely offset by the early dying 
out of the bark of the burl exposing the wood. It is an observed fact, 
experimentally proved by the writer, that strongly suppressed yellow 
pine, larch, and Douglas fir do not as readily form traumatic wood 
or exude the normal quantity of resin on being wounded on any part 
as do normal, healthy trees. Such a tardy reaction to injury does not 
afford a ready antisepsis against the entrance of fungi which may 
attack these trees. Since turpentine orcharding is becoming more 
extensively practiced in the West it would be an interesting experi- 
ment to determine the relative flow of pitch from trees strongly sup- 
pressed by mistletoe and from those in a high state of health. 
RELATION OF MISTLETOE INJURY TO INSECTS. 
In the same manner that burls and other types of mistletoe injury 
on some conifers are open doors to fungi, they are found to afford 
a ready means of entrance for some species of forest-tree insects 
which do not in this region habitually attack vigorous unwounded 
trees. Old mistletoe burls on larches are almost invariably attacked 
by borers (figs. 23 and 24), and burls on yellow pine are, in the ex- 
perience of the writer, quite as frequently infested by bark and wood 
boring beetles. In this connection a very curious and interesting phe- 
nomenon often occurs on young yellow pines from 10 to 20 years 
of age. An infection by mistletoe will have occurred, completely 
enveloping the trunk some 2 or 3 feet from the ground. The parasite 
having advanced somewhat each way from the point of original 
infection, the intervening space is attacked by Dendroctonus valens 
Lec. The combined influence of the beetle and mistletoe results in the 
complete infiltration with resin of the space between the two edges 
of the advancing mistletoe, so that the cambium dries out and dies. 
Strange to state, this does not always Inll the tree. The crown goes 
on manufacturing food materials, bemg supphed with water through 
the inner wood of the girdled area. The elaborated food not being 
able to travel downward, since the cambial tissues of the entire cir- 
cumference of the stem have been destroyed, is stored just above the 
