690 
BOTANY: A. R. C. HAAS 
35°C. for 70 minutes (the time, as found by determining the electrical 
resistance, which was required to produce death). At the end of the 
exposure the rate of respiration in sea-water (at 16°C.) had fallen con- 
siderably below the normal. This might be expected, as the oxidases are 
usually injured or destroyed by heat. 
Preliminary experiments in which the electrical resistance was de- 
termined showed that the tissue was killed by drying for 135 minutes in 
strong sunlight in a current of dry air. Pieces treated in this manner 
were washed for 15 minutes in sea water and the rate of respiration was 
then determined. It was found to be about five times the normal rate. 
In the course of about two hours it fell to the normal. 
As it is well known that wounding,^ especially if severe, may cause a 
considerable rise in the respiration, it appeared advisable in this con- 
nection to make such experiments with Laminaria. The normal respi- 
ration in sea-water was first determined. After the tissue had been 
finely macerated (by means of a broken Pyrex glass-tube) on tested filter 
paper, it was rinsed from six to ten times with sea-water to free it of CO2 
and of any liberated pigment. The rate of respiration was then de- 
termined in sea-water. It was found that the injury cased a doubling 
of the rate which at the end of an hour was still above the normal. In 
this case the time of death could not be determined. 
It is therefore evident that a considerable variety of killing agents 
raise the rate of respiration above the normal and that this increased 
rate may be maintained for some time after death. The fact that the 
rate eventually falls below the normal may be due to exhaustion of 
readily oxidizable materials or to destruction of oxidizing enzymes or to 
other causes. 
That previous observers have not found a post mortem rate of respi- 
ration which is greater than the normal is probably due to the fact that 
the time of death was not accurately known and the observations were 
not commenced until the rate of respiration had sunk below the normal. 
It seems reasonable to suppose that if the rate of respiration is raised 
above the normal by an injurious agent it will not suddenly drop below 
the normal at the moment of death, but will decline gradually, as is the 
case in these experiments. 
Summary. — The respiration of Laminaria may be much greater after 
death than in the normal condition. This is the case when it is killed 
by alcohol, acetone, ethyl bromide or formaldehyde as well as by wound- 
ing, drying and other means. 
