Experiment Station Record, Volume 5, 1893-1894 Page: 58

                                
5t8                kEXPERIMENT STATION RECORD.
through it. This may continue until the protoplasm is killed by the increase and
diffusion of these substances.
This study of the environment of the plants under these conditions of forced culture
and the operation of the natural forces and physiological processes leads irres
istibly to the conclusion that this affection of the tomato plants is a physiological
one.
Having reached the conclusion that the disease was due to an excess
of root pressure over transpiration, the author took cuttings, and, by
means of rubber tubing, cork, and wax, connected them with the station
water supply. After subjecting the cuttings       for several days to the
pressure of the water at 20 to 30 pounds, the same turgidity appeared
as is shown in the earlier stages of the disease.    A cultural test was
also made on four lots of plants subjected        to varying conditions.
Wherever the conditions approached those of the greenhouse, the
cushions were formed.    Similar developments have been observed upon
various plants by different experimenters, reference to whose work is
given.
The author's summary for practical purposes is as follows:
The oedema of the tomato is a swelling of certain parts of the plant brought about
by an excess of water which stretches the cell walls, making them very thin and the
cells very large. The excess of water may be so great that the cell walls break
down, and, that part of the plant dying exerts an injurious influence in adjacent
parts.
The excess of water in the tissues is favored by the following conditions:
(1) Insufficient light.-The long nights of the early winter months, numerous cloudy
days, and in part, the walls and framing of the forcing house deprive the plants of
needed light. By a process known as transpiration, plants are relieved of much
water when well lighted, but in poor light, since the roots are absorbing water, it is
apt to accumulate to excess. Well-lighted parts of the house then should be selected
for the tomatoes.
(2) Too much water in the soil.-Water in excess can be withheld from the soil to
prevent trouble, and yet leave enough for the plants to grow.
(3) The temperature of the soil may be too near that of the air.-A high temperature
of the soil makes the roots active, and if the temperature of the air is not considerably
higher an excess of water is apt to accumulate in the plant. The aim would
be then to have the temperature of the air considerably higher than that of the
roots.
Lack of proper light also brings about the following harmful conditions:
(1) Acids in the plant accumulate in the dark and in strong light they decrease.-When
there is an abundance of water in the plant these acids draw large quantities into
the cells, causing the cells to swell, resulting many times in lcdema, or in the killing
of the protoplasm so that these parts of the plant die and become brown or
black.
(2) Lac7c of light causes weak7 cell walls.-It is only when well lighted that plants are
capable of .making substances to build up cell walls with. Therefore, lack of light
not only favors the accumulation of water, if other things are favorable, but it prevents
the plants from building up strong tissues. In such cases plants can grow
themselves to death. Possibly artificial light might be used to advantage.
A quiet and close atmosphere also favors the accumulation of water in the plant.
Good ventilation should then be secured. Some means for the artificial agitation or
exchange of the air at night might probably be profitably devised.
Varieties of tomatoes most subject to the cedema.-Those with a tendency to a very
rapid and succulent growth are more liable to the trouble. Tomatoes which develop
a firm, woody young stem are less liable to it.