JOURNAL OF AGRICULTURAL RESEARCH 
Vol. XXVI Washington, D. C., November io, 1923 No. 6 
FURTHER OBSERVATIONS ON THE OSMOTIC PRES¬ 
SURE OF THE JUICES OF THE POTATO PLANT 1 
By B. F. Lutman 
Plant Pathologist, Vermont Agricultural Experiment Station 
INTRODUCTION 
The observations made by the author 2 during the summer of 1918 
have been continued during 1919, 1920, and 1922, and greenhouse 
readings were taken in 1921. The data obtained from juices produced 
during seasons of varying character and from a number of varieties of 
potato will extend the knowledge of one internal factor of annual plants, 
since no previous investigation seems to have covered such a lengthy 
period of time for one plant. Unfortunately, it was not possible to make 
any cryoscopic determinations during 1921, owing to other work; this 
was particularly regrettable, as 1921 was a very good year for the pro¬ 
duction of physiological tip burn of typical form. 
As the literature on this subject was discussed in the report of the 
earlier work, it is unnecessary to refer to it here. It may be stated, how¬ 
ever, that the work in 1918 was an attempt to ascertain whether the in¬ 
ternal osmotic pressures of the juices from different parts of the potato 
plant varied in such a way as to be a possible factor in the production of 
tip bum. The readings seemed to show that although the juice of the 
growing leaves has a higher osmotic pressure during the early part of 
the season, the stems attain a still higher pressure as a result of the 
accumulation of sugars in the sap during the height of the activity of 
the plant, when the flowers and young tubers are being produced. It is 
just at this time that tip bum of the physiological type appears. 
The writer is again indebted to Mr. R. L. Gale for the sugar determina¬ 
tions made in 1919 and for assistance in the cryoscopic determinations 
during that year. The methods used have already been described. 
The results obtained, while probably not absolutely accurate, as the 
material was not frozen before grinding and no pressure was used in 
extracting the juice, will give a fairly correct determination, as the 
same methods were used throughout and the readings obtained were made 
for comparison with each other only. These data are shown in Tables 
I, II, III, IV, and V. 
1 Accepted for publication Mar. 3, 1923. 
2 Butman, B. F. osmotic pressures in the potato plant at various stages of growth. In Amer. 
Jour. Bot., v. 6, p. 181-202. 1919. Literature cited, p. 202. 
Journal of Agricultural Research, Vol. XXVI, No. 6 
Washington, D. C. Nov. 10, 1923 
aff Key No. Vt-3 
60377—23-1 
(243) 
