54 BOTANICAL GAZETTE [JANUARY 
ature. The temperature was obtained, as previously, by taking 4 
the average of the temperatures recorded by the self-registering 
thermometer. After steaming, the diminishing transpiration can- 
not be due to decrease in temperature, since the temperature on the _ 
first day after killing the stem was the same as on the last day 
before steaming 10 cm. In table VI the average daily temperature 
gradually rises, while the transpiration diminishes from day to day, _ 
until on the last day (May 27) it is only 0.4 gm., having fallen _ 
off from 1.7 gm. on May 23. The weather conditions are recorded _ 
in order to show that decrease in transpiration is more dependent — 
on the stem having been steamed than upon the changes of tempera- 
ture and light. : 
It is evident from these tables that the amount of water tran- _ 
spired after steaming 10 cm. of the stem of Cyperus is very much — 
less than before the treatment. The difference in temperature — 
and weather conditions must be taken into account, but they are 
probably not sufficient to account for the very great difference 
in the amount of water given off in the two cases. In table V the 
average temperature record is higher than in table VI, and there 
was more clear weather, but these differences do not account for 
the immediate and continued slowing down of the transpiration 
rate as shown in table VI. The amount (1.7 gm.) transpired 
during the first 24 hours after steaming is far below that of any 
corresponding period before treatment. On a very cloudy day; 
at a temperature of 18° C., the plant gave off 2.9 gm. of water; 
while on a very bright day, at a temperature of 25° C., it transpired 
only 1.5 gm. after a section of 10 cm. had been steamed. }t is. | 
plain that steaming 10 cm. of a stem of this plant very soon affects _ 
in some way the amount of water given off by the leaves. , 
In fairly mature shoots of Cyperus, the amount of water given” 
off by the leaves in-a given time may be assumed to be approx: 
mately equal to the amount absorbed by the roots. Therefore, the 
steaming must in some way interfere with the amount of water” 
that passes through the killed portion, as well as that given off 
by the leaves. There is of course an almost immediate withering 
and shrinking of the steamed portions of the stem; if this region 
is exposed it soon drys out also. Careful weighing shows that 
ee 
