tgit] OVERTON—TRANSPIRATION AND SAP-FLOW 45 
their plasmolysis. I have further experimented in the same way 
with cut stems, in order to compare the amount and rate of 
transpiration with that of stems treated in the same way but kept 
in connection with the roots. Since several recent workers have 
raised objections to the use of cut plants in such experiments, 
this point is worthy of careful consideration. Throughout the 
investigation, all plants were kept as nearly as possible under 
similar conditions of light, temperature, and moisture. 
To determine the amount of water lost per unit area of leaf 
surface by the umbrella plant as compared with other common 
forms such as Helianthus annuus, potted plants and plants grown 
in culture solutions were used. In such experiments all of the 
stems but one were cut away, and the soil and pot were then so 
inclosed as to allow no loss of water except through the leaves. In 
case of plants grown in culture solutions the corks were sealed in. 
For these cultures 500 c.c. wide-mouth bottles were used. Flat 
corks to fit were split and fitted about the stems of the plants after 
they had first been wrapped with cotton wool for protection. The 
corks were sunk about 1 cm. below the edge of the bottle, so that 
melted wax could be poured in when it was desired to seal in the 
corks. The plants were grown in Knop’s nutrient solution as 
given by Detmer. Leaf areas were determined by using East- 
MAN’S ferro-prussiate paper; the white areas were cut out and 
weighed. By obtaining the weight of 1 sq. cm. of the blue print 
paper, the areas of the leaves were easily obtained. In order to 
determine whether the paper was uniform in weight, several 
weighings were made. The average weight of 1 sq. cm. was used 
’ as the unit in calculating the leaf areas. This of course must be 
doubled in determining the transpiring area if stomata are on 
both sides of the leaves, which is not the case in the normal plant. 
In order to calculate the rate of motion of the transpiration stream, 
the lithium method as described by Sacus (25) for rooted plants, as 
well as the eosin method, was used. In the latter case the rise 
of the eosin in the stems and leaves of cut branches was observed, 
as is easily possible in the umbrella plant by the aid of the hori- 
zontal microscope. ‘ 
Some of the experiments described by UrspRUNG and RoSHARDT 
