Igtt] OVERTON—TRANSPIRATION AND SAP-FLOW 29 
and on stems of Vicia Faba, Phaseolus multiflorus, Hedera Helix, 
and Fagus silvatica. By treating short stretches (1, 2, or 3 cm.) 
of the petioles of Primula with steam for 3 minutes, he found that 
no immediate, visible effect is produced on the leaves; while if 
longer portions (6-9.5 cm.) are killed, wilting follows in about 
4 hours. These observations are further supported by similar 
experiments on Pelargonium, Begonia, and Impatiens, from which 
he finds that the leaves wither more and more rapidly as the lengths 
of the killed portion are increased, even when the killed region is 
protected, and this shows, according to UrRsprunG, that wilting 
is not due to a lateral evaporation in the killed portion, but to a 
lack of sufficient water supply. He finds no stoppage of the vessels 
as the result of treatment. If stoppage of the vessels were caused 
by the treatment, he believes the leaves would wither as quickly 
above a short as a longer killed region. 
For the study of sap-flow in stems UrspRUNG chose three plants 
of Phaseolus as nearly alike as possible. Removing all except the 
two topmost leaves, he killed the stems of two plants for 40 cm. 
above the soil, leaving 20 cm. untreated below the leaves of one 
plant. The killed portion was left exposed, while the other was 
covered with paraffin. The leaves on both plants wilted in 2-4 
days, being entirely dry in 4 days. The leaves of the unprotected 
plants wilted faster. A plant 63 cm. high was killed for 22 cm. 
above the soil; the leaves remained turgescent for 19 days. From 
these and other experiments on Phaseolus he concludes that the 
longer the killed portion ofthe stem, the sooner the leaves above 
wither, and that the living cells are necessary to the elevation 
of water in sufficient quantities. On killing 80 cm. of a rooted 
stem of Hedera, the youngest leaves were observed to wilt in 1.5 
days. Leaves situated below the killed region were not affected. 
Histological examination failed to reveal any stoppage of the 
vessels. In case of the stem, withering in Fagus could be observed 
in 2 days when 80 cm. of the stem were killed, while the leaves 
remain turgescent for 20 days when only 3 cm. were killed. In 
repeating some of his experiments on Fagus, he (34) observed that 
wilting and discoloration in spots occurred on the leaves. Similar 
discoloration was also observed when leaves were simply deprived 
