There is an example of this within three minutes' walk of
this building. Here are the climatic and temperature conditions that
bring about disaster, particularly if preceded by a dry season. Let us
start with a dry season. The season of 1911 was conspicuously dry in
this locality and the adjacent states of Virginia, West Virginia and
Maryland, but about the first of September the rains came. Up to that
time even the native forest trees such as oaks and chestnuts showed the
stress of lack of moisture very seriously and were somewhat yellow and
pale looking, mainly from water and nitrogen starvation. When the rains
came the wilted trees all greened up, every tree in the parks brightened
up, and we had fine growing conditions until October and no cold weather
up to New Year's. It was warm that fall and even on New Year's day the
warmth was noticeable. On the 12th of January we had the record cold
temperature for this locality in the history of the weather bureau,
except one year. We had fifteen or seventeen below zero and it was as
low as thirty-eight in low spots in the Potomac Valley in West Virginia.
Those trees had never been fully shocked into winter conditions. The
cambium growth and sap flow had not been stopped and the physiological
changes needed to get the trees ready for cold weather had never
occurred. They were not ready, not only as to the bark, but in the trunk
and wood. The result was that the trees were seriously injured, the less
matured twigs died back, and the trees were frozen on the trunks down to
the ground line. In the freeze of 1904 in New York I was surprised to
find that the peach trees were not all killed. They were frozen through
and through and yet the trees did not die. The question of winter injury
hinges not alone on low temperature, but it also depends on the
condition which the tree has reached when the cold strikes it. Now, to
tell you still further about what that cold wave did, I will ask you to
look at that row of red oaks near the Smithsonian which I just alluded
to and see the big ribs of dead bark where the cambium layer has been
shocked, and checked in other places. You will find these trees ribbed
and ridged to about half way down the row. Those trees are subject to
special disadvantages; they lack subsoil drainage and they have an
excess of manure draining down through the paving stones. They have an
excess of nitrogen and lack of drainage. The subsoil is a heavy clay.
That bring