re in use, and which I shall not
discuss.

With reference to stimulation of cellular activity we are considerably
concerned. In medicine I have found the subject of wound repair and
immunity most interesting, the two subjects seeming to be more or less
related. Some animals will repair wounds and immunize readily, while
others will not. In a general way young healthy animals and human
beings immunize most readily, while older ones frequently fail almost
entirely. Interestingly enough plants seem to be strangely similar in
this respect, and the thing that stimulates cellular activity for
defensive purposes (immunity) apparently stimulates growth and wound
repair. The thing that stimulates most actively for a special purpose is
the thing itself, the best stimulant for wound repair being the simple
injury. To illustrate briefly: In my work last summer I came in contact
with two enemies, yellow jackets and copperheads. The copperhead
stimulated me to carry a club in defense, while for the yellow jacket
the club was of little value and I rather preferred carbon bisulphide.
Had I ignored my senses and allowed nature full sway, as a tree does,
the snake would have injected his venom and the yellow jacket his toxin,
and my cells would have accepted their only alternative and proceeded at
once to build up a specific defense, after which they would have been in
better shape for development, providing the poison would not have been
so great as to prove fatal. Injury to a tree certainly does stimulate
wound repair, defense and growth. It is well known that trees with many
transplantings, root injuries, transplant much more readily, and the
nurserymen use this method of stimulation as a routine procedure. I
learn in Florida that in order to transplant a good size palmetto, they
are in the habit of digging down on one side and cutting the roots the
year before removal. It will then transplant more readily. Pruning has
the same cell stimulating effect if done at a time that will retain the
stored nutrition. An attack of disease just as surely stimulates
cellular activity and growth but it is too frequently followed by
disaster.

We have all heard of driving rusty nails into trees (thinking the iron
produced the beneficial results), cutting a slit in the bark of the
limbs and trunk for "bark bound" so called, etc., all of which have
stimulating effects with more or less permanent injury to the tree. Who
knows but what the sap sucker,