66 J. H. Priestley and Dorothy Armstead 
and that in all probability Pitra’s observations must find their 
explanation in osmotic phenomena. Stems killed by prolonged ex¬ 
posure to chloroform or by exposure to steam show no exudation 
pressure, which indicates that the phenomenon is dependent upon 
the living semi-permeable membranes of the protoplasts around the 
xylem. Copeland’s views receive further justification in the results 
of a simple experiment several times repeated of which two examples 
are cited. 
Lilac stems with leaves attached were set up with capillary tubes 
attached to their cut ends. Behind the capillary tube a glass scale 
was clamped. The level of the meniscus was read at frequent intervals 
by means of a telescope. After about an hour, the water from the 
glass vessel in which the stems were placed was siphoned off, and 
replaced by 5 per cent, salt solution, the level again read at intervals, 
and then the salt again replaced by water. In this way any change 
in the amount of liquid excreted into the xylem from the surrounding 
parenchyma and passed up into the tube, could be ascertained. 
The movement of the meniscus is illustrated by the figures shown 
below: 
Twig in water 
Time 
Height of 
hrs. mins. 
meniscus 
2.30 p.m. 
2-25 cms. 
2-34 » 
2-30 „ 
2.38 „ 
2-38 „ 
2.42 ,, 
2-42 ,, 
2.46 ,, 
2-47 .. 
2-54 .. 
2-60 ,, 
3 -o „ 
2-70 ,, 
3-26 „ 
300 .. 
3-32 „ 
3-20 ,, 
3.32 water replaced by salt solution. 
3.45 p.m. 
4-25 cms. 
3-49 „ 
4 45 „ 
3-56 » 
4-40 .. 
4.0 „ 
4-15 .. 
4-4 .. 
3-90 „ 
4.10 ,, 
350 „ 
4-14 .. 
3-20 „ 
4-38 „ 
i-8o ,, 
4.46 „ 
1-30 „ 
.50 salt solution replaced by water 
4.55 p.m. 
10 cm. 
4-57 .. 
120 cms. 
5-4 .. 
170 
518 „ 
2-70 „ 
5-30 „ 
3 - 4 ° 
5-52 „ 
390 „ 
