September, 1916 
WISCONSIN HORTICULTURE 
13 
location and the more or less ex- 
tensive areas irregular in outline 
and frequently aggravated by the 
attacks of disease spores or in- 
sects, especially the plant lice. 
In young trees, perpendicular 
cracks may run up from the 
ground line and become so 
serious as to girdle the tree in the 
spring growth. Bridge grafting 
may be resorted to with uncer- 
tain results, and the trees are 
best replaced in severe cases. 
Snow or other ground covers will 
usually prevent the occurrence of 
such injuries. 
The Cankers, though due to a 
possibly wider range of causes, 
also resemble Collar-rot in being 
started chiefly by winter injury. 
The aerial parts of the tree may 
be injured in many cases where 
the roots and crown are but little 
affected. Various theories have 
been advanced as to the cause, 
such as: Tensions in wood of 
vigorous growth which is ex- 
posed to high, drying winds, or to 
strains at the crotches with dry- 
ing out of tissue and consequent 
cracking under tension. More 
recent observations at the Mis- 
souri Station conducted by Dr. 
Whitten have shown a great ab- 
sorption of heat on the south 
side of the tree in sunlight with 
extreme drops in temperature at 
sundown. From his Records of 
temperature drops from 70 de- 
grees (Fah.) to atmospheric 30 
degrees within very short inter- 
vals at sundown, his explanation 
seems well-founded, especially 
where the wood is immature. 
Hardiness in a plant may be 
considered essentially as its abil- 
ity to withstand unfavorable 
environmental conditions, espec- 
ially as regards temperature. 
This is largely determined in the 
species and the variety of plant 
but it may be materially affected 
by those influences which bear 
directly upon the maturity of 
the wood. Recent observations 
indicate that there is a state of 
rest in the early period of 
dormancy during which trees 
will not in general be affected 
and this period is much longer 
in the case of properly matured 
trees. Alternate freezing and 
thawing with excessive drying 
tend to break this rest period 
with its resultant liability to 
injury. If then we can increase 
the moisture holding capacity of 
the soil, maintain a more uni- 
form soil temperature and aid 
materially in lessening changes 
in such conditions, along with an 
increased maturity of the wood, 
we can largely prevent an early 
break in the rest period and 
thus increase the hardiness of 
the tree. 
In our cultural methods for 
preventing or lessening these 
forms of injury we may now 
understand the conditions that 
will reduce them to a minimum. 
As we have seen in nearly every 
case of injury, the maturity of 
the wood has played a most 
important part and our methods 
should be directed to securing 
this primarily. We must further 
provide a protection to the roots 
in a ground cover, which will 
prevent deep freezing and dessi- 
cation as well as retard growth 
in the spring or during un- 
seasonable warm spells. The 
(Continued on page 15) 
Let George Do It 
Or Paul or Howard or 
even Gladys. Any boy or 
girl can get one or more 
new members without 
going far from home. 
A Cash Offer 
During September only 
a cash bonus of twenty- 
five cents will be allowed 
for each new member 
secured . 
Collect 50c for each 
m embershi p, send 
twenty-five to this office 
and retain balance. 
Let the Young Folks Do It. 
No renewals. No post- 
age stamps. Send for 
sample copies, coin 
cards and self-addressed 
envelopes. 
F. Craneficld, Sec. 
SALESMEN WANTED! 
We are in want of a few T reliable, energetic men to 
act as agents for the sale of our Northern Grown Trees, 
Shrubs and Vines from our Nursery. Previous experience 
not essential; live active men can earn good wages. For 
our terms address, giving full name, age and reference, 
GREAT NORTHERN NURSERY CO. 
Baraboo. \A is. 
