Curtis: SoME OBSERVATIONS ON TRANSPIRATION 363 
weighings exactly at the end of the hour if the various measure- 
ments were to be of any value. It is apparent how imperfect a 
knowledge of the transpiration rate or how misleading may be 
the results when observations are taken at long or irregular inter- 
vals or fora short period and from such data drawing conclusions 
as to the rate. 
For the purpose of comparison a number of experiments were 
conducted under more uniform conditions. The records found in 
Table II. were obtained in the dark room where the plants were 
exposed to an electric light of g00 candle power hung at a dis- 
tance of 4 m. from the balance. The dark room was sufficiently 
light-tight to permit the handling of the most sensitive photo- 
graphic plates without injury. When necessary the humidity was 
controlled in a degree by sprinkling the floor and the tempera- 
ture rarely varied more than one degree. In this and the preced- 
ing table where the record of two plants are given at the same 
time two separate balances were used to avoid a possible error 
due to distributing the plants in moving them. Baranetsky’s con- 
tention on this point has something of merit. Certainly with the 
most careful manipulation the operator runs a very considerable 
risk of disturbing the delicate balance in the plant and in a con- 
tinued series of observations it is at least questionable whether 
the results obtained in this manner may always be relied upon. 
The plants in these experiments were usually placed in the dark 
room over night or for two or three hours before using. This 
permitted an adjustment to the conditions obtaining in the 
room and eliminated such after effects as have been noted by 
Schwendener and Sorauer. Buds and young leaves were cut 
off in many of the cases cited about one week before the ex- 
periment ; in other instances such parts were sealed with a mix- 
ture of beeswax, tallow and linseed oil and then bound with 
Sheet rubber. The interesting results obtained by Hoehnel on 
the relative transpiration rate of young and old leaves and simi- 
larly by Wiesner on the transpiration of developing stems and 
also of Sorauer on the relation of the formation of chlorophyll to 
the transpiration, renders it necessary in arriving at any conclu- 
Sion as to what the plant is really doing to exclude such factors 
aS may introduce variations that would furnish misleading results 
