1908] FREEMAN—DETERMINATION OF TRANSPIRATION 11g 
transpiration rate as compared with the same plants growing in the 
soil, four species were selected which seemed to promise a large range 
of difference in transpiration. Accordingly, two individuals of each 
of the following species were selected from young potted plants in the 
greenhouse: Coleus Blumei, Chrysanthemum leucanthemum, Pelar- 
gonium sp., and Portulaca oleracea. The plants to be used on their 
own roots were repotted into glass tumblers of suitable size. This 
was done without disturbing the root system. Evaporation from the 
soil was prevented by covering the tops of the glass with a good 
‘ quality of dental rubber. 
For the potometers the plants were cut from the pots at the sur- 
face of the soil, one or two of the lower leaves removed, and the stems 
inserted, through holes in the cork, into bottles containing tap water. 
The whole stopper was then carefully sealed with paraffin. Each 
potometer was placed by the side of its corresponding potted plant and 
the whole series left on a table in a well-lighted room. 
During the investigation, which lasted approximately sixty hours, 
the transpiration rate was found by weighings made at intervals of 
about one hour during the day. In Table I the average transpiration 
rate for each plant during the whole of the experiment is shown, and 
the transpiration rate of the plants on their own roots (normal) is 
compared with that of the plants in the potometer by reducing the 
latter to percentages of the former. 
TABLE I 
Potted plants on | Cat stems in. pot- Cut stems in 
oots; trans meter; transpiration) ee 
cent. 
pation i ng pe | ing prom | De cent 
surface per hr. per hr. transpiration 
Oe OEE ee 7.21 1.44 = 
COIR a 05s ees 2.77 0.37 13-3 
Porttalacasss 3 cos eet 1:72 0.47 27-3 
Geranium ood: ees, 8 0.65 0.65 
It will thus be noted that there is a great difference between the 
average transpiration rate of a plant on its own roots and that of a 
cut stem of the same plant placed in water. Moreover, roughly 
speaking, this difference is greatest in those plants having the highest 
normal transpiration. This difference, however, may vanish alto- 
