48 BOTANICAL GAZETTE [JANUARY 
The temperature was obtained by averaging the daily record as 
registered by a RicHARD thermograph. It is seen from the table 
that a plant giving off 18.6 gm. of water per day through its 
leaves and stem will transpire 2.2 gm. only through its stem. 
Observations with lithium nitrate show that water rises in — 
stems of plants in nutrient solutions whose tops have been removed, 
at the rate of about 150 mm. per hour. Sacus (25) concluded 
that the transpiration current travels at the rate of 63 cm. per hour 
in Helianthus annuus, and that the rate of sap-flow varies greatly 
in different plants and in the same plant under different conditions. — 
The method of measuring the rate of sap-flow by setting cut stems 
in dyes and observing the rise of the colored solution has been 
criticized by Sacus, who showed that the water travels faster than 
the dye. A more exact method used by him consists in watering — 
the entire plant with a solution of some lithium salt, or adding the — 
salt to nutrient solutions, and ascertaining by means of the spectro-_ 
scope how far the salt rises in a given time, thus obtaining the rate — 
of flow. 
TABLE III 
SHOWING THE RATE OF SAP-FLOW IN ROOTED PLANTS AS DETERMINED BY 
SACHS’S LITHIUM METHOD 
Length of plant Sag tieaneg to suc ue sits Poon 
73 cm. 24 min. 3.04 cm 182.4 cm 
50 cm. 20 min. 2.50cm 180.0 cm 
45 cm. 15 min. 3 m 180.0 cm 
48 cm. 17 min. 2.82 cm 145.2 cm 
cm. | 20 min. 2.60 cm 156.0cm 
41 cm. 15 min. 2.73 cm 163.8 cm 
36cm. |. 23 min. 2.76 cm 165.6 cm 
29cm. | ro min. 2.90 cm 174.0 cm 
60 cm. | 15 min, 4.00 cm. 240.0 cm 
47 cm 12 min. 3-91 cm. 234.6 cm. 
35 cm | To min. 3-50 cm. 210.0 cm 
In obtaining the data tabulated in table III, I have employed 
Sacus’s lithium method, and find that the rate of sap-flow ™ 
hour. In cut plants the flow is slightly more rapid, the extremes 
being 180 and 250 cm. per hour. In comparison with Helianthus, 
