20 BULLETIN 1465, U. S. DEPARTMENT OF AGRICULTURE 
A very considerable and confusing error would have been intro- 
duced by failure to consider the temperature of the air at the time of 
weighing. The spring of the balance was markedly affected by changes 
in air temperature, often to the extent of 2 kilograms or more. It 
became necessary to choose a time of day when the sun did not strike 
the balance and when the temperature was comparatively low. 
Screening the balance was tried, but without material success. In 
order to have a temperature which could usually be attained through- 
out the growing season, 60° F. was selected as the correct air tempera- 
ture for the operation of the balance. The weighings were usually 
made in the morning if the eastern sky was hazy or there was other 
shade. Occasionally weighings could be made during a cloudy day or 
after sundown. It was impossible to weigh during the day in full sun. 
In weighing, the balance was always tested against a known dead 
weight, and if the correction necessary was small, the weighings were 
made and corrected. The cans were not weighed every day, so 
that a time could be selected without any experimental injury because 
of postponement. 
GROWTH OF PLANTS 
The growth of the plants was feeble, even under what appeared 
to be the optimum conditions. At no time was there anything 
approaching a normal rate of growth, the plants growing usually 
only a very few inches during the entire season. On some plants 
the leaves were yellow and small and, although showing no signs of 
contamination or disease, were obviously devitalized. The lack of 
vitality appeared to be caused in part by the soil, the humus of 
which had been destroyed by the steam. What toxic substances 
were present in the soil is not known. Also, the plants were defi- 
nitely hurt by the process of paring, which took away the best part 
of the eye. From this loss they seemed never to recover. Add to 
these destructive influences the exposure to unfavorable tempera- 
tures, and it is evident that the plant growth must have been weak 
indeed. Plate 5 shows a small sterile plant emerging from the hole 
in the cover into the chimney. Plate 6 shows a plant as large as 
any obtained, but even this developed no special sturdiness. 
That these plants were sterile is attested by the sterility of frag- 
ments of leaves and roots planted in potato and beef agar. The 
potato seed piece practically disappeared, but no contamination of 
it was detected where the leaves and roots were sterile. 
INOCULATION 
No plants were obtained which could be used for inoculation with 
Fusaria. This was to have been attempted through the hexagonal 
opening in the cover. It was expected also that the plants would 
attain a size sufficient to permit the removal of the chimney from 
around them and the sealing of the plant in the hole of the cover. 
The methods and materials were perfected for sealing this joint but 
were never used in actual practice. 
RESULTS 
The immediate experimental aim to grow and maintain entire 
potato plants in a sterile condition during the span of a normal season 
was achieved. Plants were produced from sterile seed pieces and 
