8 J. -K. WILson 
plants fourteen days old was used, also was positive though not so pro- 
nounced. 
Tests of this character using water from maize fourteen and eighteen 
days old gave no increase in nitrites. | 
| 
HYDROGEN ION CONCENTRATION OF WATER FROM HYDATHODES 
It was pointed out by Haas (1920) that the hydrogen ion concentration | 
in expressed sap of plants varies with the kind of plant, its stage of maturity, 
and the substratum on which it was grown. In this work it was desirable 
to know whether or not the exudate water of young plants would vary 
in hydrogen ion concentration in the same way. In order to throw light 
on this point, maize, oats, and timothy were grown under sterile conditions 
on the same kind of substratum, and timothy was grown also on five 
different kinds of substrata. The exudate water was removed from all 
the plants each day, and the hydrogen ion concentration was determined 
by the colorimetric method as published by Clark (1920), with the slight | 
modification that the exudate water was placed in the wells of a spot. 
plate and a small amount of indicator was added to each. The resulting 
colors were compared with Clark’s color chart to determine their pH 
value. The findings are recorded in table 2: 
TABLE 2. Hyprocen Ion Concentration oF ExupATE WATER FROM MazzE, Oats, 
AND TIMOTHY 
(Plants seven days old at time of first collection) 
Maize Oats Timothy 
Number of days after 
first collection Sub- Sub- Substratum * 
stratum * stratum* 
1 1 2 3 4 5 
pH pH jolakel eo yovel pH | pH | pH 
pee ts Pa osteo a ni cia 8.2 6.3 6.6 6.8 7.0 6.8 | 6.8 
AGS te RSE Se Rae Neo ee 6.2 6.4 6.2 6.8 CO) OY 6.6 
DRS Paths eect a eho BU og 6.4 6.6 6.2 6.6 6.6 Gees GE 
SS DLN tC Span Ml ate coy Ree nar 6.4 7.0 6.4 5.8 GG) 4} Oats) | ORO 
Zs RAL Nea gee eae he rae Si? 6.4 5.6 5.6 6.4 | 6.8 Wea, 
Lg des eee seem tah oe Ie sat ata, Dee, 6.6 624. |). 16249 |e eae | ee 
Giri Sirs ornare aR fee! Onan HG} 6.6 6.2 6.2 G28 | erent | ai ne 
ULI WEI dts te tes eR Os ere aR 6.4 6.4 6.2 aH ee Sh Sie es 
SOM a epee tae ae ama Ne aay Ai3 BLD es 5.6 6.2 6.2 6... 2a a Re ee 
ORT Se aed eI en PRN a A ek a 5.0 oe 6.2 T ANS | eee | eee ee 
HO PRON Oe eat area on atin 5.0 (ce aaa erence I oo. cllaw anes 
ANGI Pa ivan’ Aone ean ae epee Nahe bea! ioe Mena Wena Wa Il Sel so ailbiiees < 
PaO SAROA SS epee RS, Me als 6.2 7.0 6.2) 3. ees Gxt 6a 
SPOR ARVIN SMC MERIT. - fu an Ty GD Raed Spee eh a 7 ODN eae 6.9 6225 | Hanalei 
ASR ce gach tia tre Nes Amey ai CG yeN 6 tee a ee Nn RN lc 5 5.0 alles oc 
* Substratum 1, full nutrient solution plus 1.5 per cent of agar to solidify; 2, distilled water and 1.5 
per cent of agar to solidify; 3, soil with 30 per cent of full nutrient solution; 4, soil with 30 per cent of § 
tap water; 5, soil with 30 per cent of distilled water. : 
It is observed that the first water exuded from the hydathodes of young | 
maize, oats, and timothy plants as measured by the colorimetric method | 
was approximately neutral and that as the plants became older the exuded 
water became more acid. In the case of maize this acidity increased 
