FORMATION OF OVERGROWTHS 
213 
These values are free from errors arising in expression of the juice and 
represent the true freezing points of the tissue. They are of greater value 
than those made on expressed sap because small pieces of tissue can be taken 
immediately adjacent. Since such good checks were obtained, the author 
is inclined to believe that there is but little difference in the osmotic con- 
centration in these particular cases. 
Juices expressed from tumors produced by inoculation with Bacterium 
tumefaciens show a hydrogen-ion concentration consistently a little lower 
than that of juices expressed from healthy stem tissues taken from adjacent 
nodes, as shown in table 3. 
Table 3. concentrations of tumor and healthy tissues 
Ricinus 
Ph 
Ch X io« 
Tumor juice 
5-822 
1.51 
Healthy stem juice 
541 1 
3.88 
Leaf juice 
5.580 
2.63 
Tumor juice 
5.886 
1.30 
5.817 
1.52 
Leaf juice 
5.739 
1.82 
Tumor juice 
5.62 
2.40 
5-35 
4.47 
5.48 
3.30 
Beet 
Tumor juice 
6.347 
0.42 
Healthy root juice 
5.818 
1.52 
These tumors were in actively growing condition. The juice was 
expressed after grinding in a meat chopper but without freezing the tissue, 
since the hydrogen-ion concentration of a juice has been shown to be 
changed by the precipitation of the proteins on freezing the tissue. The 
determinations were made by the potentiometric method. 
It may be suspected that the expressed juice will show a H+ concentra- 
tion different from that of the cell sap of the vacuoles owing to errors arising 
by expression. This may be the case in some tissues. However, the author 
has been able to dilute the juice from such tissues as tomato fruit to one 
fifth the original concentration without appreciably changing the con- 
centration. The H+ concentration within the uninjured cells can be 
estimated only in tissues which have natural indicators. 
The concentration of the buffer salts present in the tissue will determine 
whether or not they are able to maintain the original Ph value on dilution. 
Precipitation of globulins on too great dilution of the juice may bring about 
H+ changes. The H+ concentration of a buffer solution depends (within 
fairly wide limits) upon the ratio of the buffer substances present, and not 
upon their total concentration. In obtaining the freezing-point depression, 
