38 BOTANICAL GAZETTE [JULY 
equal to one-fourth the volume of the plant. No toxic effects were 
noted for concentrations of 0.0064 N oxalic acid and below. The 
results are given in table IT. 
TABLE II 
SHOWING EFFECT OF DIFFERENT CONCENTRATIONS OF OXALIC ACID 
RATE OF ABSCISSION 
February March 
Concentration 
5} 16 8/19 3 6| 27| 28} | 2/3) 4] 5 
@.0256 N oxalic acid... ...,.. no baat Bhs vb Bie Lg} SES. 1 Gis 
wee yf Ee Ta? Se Aor 6 6 On 
6.0005" = * ee Pe I a oa eset gl SE Cie. 
0.0032 “ . st ae I cols ciicpent Ste cP Sti. ele 
9.0016 © % Spe ao an Cv BEC Eeee 2) 3| 4) S} 6. 
rete a el fd aT LC] ay of fe] ake 
Vintieated ik ei ech ky Be ae ay 8 ae i | age vei 
Mt ean an wa uo kel a sys i Jat ae Oa 8 
The plants were infiltrated February 9, and again February 22. 
Leaf-fall was allowed to occur normally under greenhouse condi- 
tions. The numbers refer to the total number of leaves off at the 
corresponding date. 
Although concentrations of 0.0128 and 0.0256 N oxalic acid 
showed marked toxic effects, abscission was not accelerated; con- 
centrations between 0.04 and o.12N oxalic acid killed many 
blades without killing the petioles and stem. In such cases 
abscission of the petioles occurred within 2 or 3 days, just as in the 
case of petiole fall after amputation of the blade, or severe wounding 
of the blade. 
Likewise direct measurements of acidity do not agree with those 
of WiesNER. Table IV gives the acidity for 9 different regions of 
the plant. Falling leaves are not so acid as green leaves. Fresh 
yellow leaves in the act of abscissing when titrated with NaOH, 
using phenolphthalein as an indicator, had an acidity equivalent 
to 0.0069 cc. of normal acid per gram of wet weight. Fresh green 
leaves collected at the same time from the same plants had an 
acidity equivalent to 0.0089 cc. of normal acid per gram of wet 
weight. In both cases the leaves were weighed as rapidly as pos- 
