376 
Journal of Agricultural Research 
Vol. II, No. s 
machine, separate experiments show that a poftion of the activity is 
lost thereby. The fresh hand-pressed potato juice had an activity of 
0.287 units (pyrogallol), while the juice pressed out of the remaining 
pulp by means of a hydraulic press at a pressure up to 15 tons on a 6-inch 
circular ram was 0.170 units (pyrogallol) and the juice pressed out at a 
still higher pressure had an activity of only 0.107 units (pyrogallol). 
Inasmuch as the juice obtained by means of the hydraulic press had to 
pass through an appreciable amount of compressed pulp, it is probable 
that the diminished activity of the machine-pressed juice was due to the 
loss of a part of the oxidases by adsorption. 
In this connection the results of Dixon and Atkins (1913) are very 
interesting. They found that in successive pressings of leaves (Hedera 
helix) in a vise, juices with increasing concentration of electrolytes were 
obtained. They experimented also with leaves treated with liquid air 
and concluded that the only way to obtain juices corresponding to the 
concentration of the sap in the vacuoles of the uninjured tissues is to 
press them out after exposure to liquid air. Unfortunately, such pro¬ 
cedure was impossible during this work, which had to be carried out 
in the field. 
RATE OF GROWTH OF THE POTATO PLANT 
In former publications it has been shown that the oxidase content of 
juices bears a very definite relation to the rate of development of the 
particular plant specimens from which they are derived. In the sugar 
beet, which the writer studied in this respect, the oxidase content of the 
foliage runs up appreciably when the normal growth of the plants is 
interfered with by drought, excessive watering, diseases, etc. In the 
foliage of normally developing sugar-beet plants the oxidase content 
of the juice is only about one-half that of stunted plants. On the basis 
of the results obtained with sugar beets the following generalizations 
can be made: 
Normal growth.Normal (low) oxidase content. 
Retarded growth.Abnormal (high) oxidase content. 
The recognition of this fact led to an examination of the rate of growth 
of the potato plants which were used in this research. Table I shows the 
relation which the size of the shoots and the foliage of all the plants in a 
hill, as well as of the single shoots, bears to the age of the plants. 
