GEO WING BACTERIOLOGICALLY STERILE POTATO PLANTS 19 
remainder of the germinative tissue and in more than half of the cases 
took all of it. These pieces were useless. Of the others, some would 
develop contamination at the eye, or molds would appear on them 
and cause them to -be discarded. Where they were of seeming 
purity and germinating in a degree, it was obvious that they were so 
weakened by the removal of bud tissue that growth would be prob- 
lematical. Generally not more than 5 per cent of the seed pieces pre- 
pared were satisfactory enough to be used. As each one took much 
time for preparation, a very considerable amount of time was 
devoted to this phase of work alone. 
EFFECT OF SOIL STERILIZATION 
The effect of sterilization on the soil was left undetermined. That 
was a subject entirely outside the scope of the experiment. That soils 
are altered by steaming is obvious, and there is a large literature on 
this subject. It was observed that potato plants grew but poorly in 
sterilized soil, even when the seed piece was of full vigor. What the 
act of sterilization contributed to the failure of the experiment is not 
known, but apparently it was an important factor. 
EFFECT OF TEMPERATURE 
By the time the cans could be planted it was nearly summer. The 
cans were set in rows of 25 each in the open, unshaded from the sun. 
The temperature in the cans under these circumstances rose during 
the day and fell at night. Because of the changing temperature the 
air pressure inside of the can had to be easily adjusted to the outside 
pressure without breaking a seal, and to effect this the vent caps 
were supplied to each can. 
It frequently happened that the temperature ranged through 45° 
F. during a 24-hour period and seldom through less than 25°. The 
average maximum was about 90° F. and the mean during the summer 
was 75°, falling as the season advanced. The potato does its best 
under cool temperatures, and being planted in cans under trying con- 
ditions, it showed no exception to the rule. A few yellow, sickly 
plants appeared, which ceased to grow in a few days and later died. 
Some of them were contaminated, but the sterile ones appeared to 
be killed by the excessive heat. 
To control the temperature better the troughs shown in Plate 3, B, 
were constructed and the water level raised to the highest possible point. 
This had a marked effect on the temperature range in the cans. 
The average maximum fell to 80° F. and the daily range to about 15°. 
The average mean was about the same as with the cans fully exposed 
and fell in the same way, as the season advanced. The potato plants 
which grew were of improved vigor and appearance and developed 
in a more normal manner. Had it been possible to maintain a con- 
stant temperature favorable to the growth of the potato, it seems 
probable that plants suitable for inoculation purposes might have been 
developed, but with the available equipment this could not be done. 
KEEPING THE WEIGHT OF CANS UNIFORM 
The cans had to be weighed with care and under known conditions. 
It was intended to maintain a soil-moisture content of approximately 
18 per cent. When the cans lost 2 liters in weight this was restored 
by the addition of water. These calculations were easily made and 
the uniform weight maintained. 
