EMERSON: BLACKENING OF BApTISIA TINCTORIA 625 
These conclusions are drawn from over fifty experiments made 
under the same conditions with the various solutions, each solu- 
tion being tried at least twice, generally more often, at each degree 
of temperature between the extremes indicated. 
A little different temperature test was made by holding 
branches with the leaves on in water at 70°, $0", 90° and 100° C. 
for five, ten and fifteen minutes, then mashing the leaves and pre- 
cipitating with alcohol and testing as usual. In this way the en- 
zyme was not destroyed until the branch had been at 90° C. for 
fifteen minutes, and even then there was a little reaction with 
hydrogen peroxide. At the boiling point of water the oxidase 
was destroyed by a five-minute exposure, the peroxidase by a ten- 
minute exposure. Even this high temperature for less than five 
minutes does not quite destroy the enzyme, and this fact was no- 
ticed with a solution which gave reactions when brought once to 
the boiling point, and ceased only when boiled several minutes. 
The leaves on the branches when exposed to the lower degrees 
for short periods turned dark or black on drying, while the boiled 
ones remained green. 
These temperature results correspond fairly well with those 
given for the maple leaf by Woods.* He found that in the plant 
tissues both the oxidase and the peroxidase will stand somewhat 
higher temperature than in aqueous or alcoholic solutions. The 
©xidase of a hard maple leaf is usually destroyed by heating five 
Minutes at 70° C. in an aqueous solution ; the peroxidase requires 
five minutes at 80° C. In the leaf, however, it took fifteen min- 
utes at 85° C. to destroy them, while both were destroyed in a 
50 per cent. alcoholic solution in three minutes at 70°-72° C. 
The enzymes of other leaves behaved in a similar manner. The 
tobacco oxidase is destroyed between 65° and 66° C. and the perox- 
idase between 87° and 88°C. On this subject Loew ¢ says: ‘‘ The 
temperatures thus far observed which render enzymes inactive are 
Not constant under all conditions; the acidity of the plant juice, 
the degree of dilution, the duration of the heating, and the pres- 
_ of certain salts have a modifying influence on the vilictin ai of 
Cen- 
. F. The destruction of chlorophyll by ciliiing een enzymes. 
* Woo 
tralbl, fi ‘Pacaale Abt. 2. 5: 745-754. 1599. 
t Loew, O, Physiological studies of Connecticut leaf tobacco, 21. 1900. 
