Physiological Studies in Plant Anatomy 67 
Similar experiments were carried out with the petiole of Spircea, 
sealed at the base with paraffin wax, and a capillary tube attached 
at the top cut end. 
Petiole in water 
Time 
Height of 
hrs. mins. 
meniscus 
10.30 a.m. 
4-65 cms. 
10.45 „ 
4-65 
1115 .. 
5-65 
.25 water replaced 
by salt solution 
11.27 a.m. 
4-40 cms. 
n- 3 1 .. 
4 ' 3 i .. 
n -35 .. 
4-20 ,, 
11.41 „ 
4-05 „ 
11.46 „ 
3-95 .. 
12.51 p.m. 
3-20 „ 
.52 salt solution replaced by water 
12.56 p.m. 
3-00 cms. 
1.0 ,, 
305 „ 
I - 5 I .. 
405 „ 
2.4 
4-25 .. 
2.30 „ 
4'45 .. 
312 „ 
4-65 .. 
3-40 „ 
3-95 .. 
3-51 
3-95 „ 
4-6 „ 
3'90 „ 
These typical results show that the rise of liquid in the tube in 
this class of experiment is controlled by the concentration of solute 
in the medium external to the plant and is therefore due to osmotic 
phenomena. 
Pitra’s earlier observations are therefore confirmed, and without 
accepting all his conclusions, his general contention is endorsed that 
stems, like roots, possess the power of exhibiting exudation pressure. 
A long series of experiments directed to the same end was carried 
out by Kraus (1C), whose usual method was to place cut twigs in 
damp sand and observe for what length of time they continued 
to bleed from various tissues at the upper end, where these 
tissues were exposed at cut surfaces. His experiments require one 
further comment. He remarks how frequently the bleeding is more 
active from other tissues (such as the pith and cortex) than from the 
xylem. A little reflection will show that under his experimental 
conditions this was to be expected. The organic solutes always diffuse 
from certain parenchymatous cells into the surrounding walls or 
intercellular space. In the uncut stem these ultimately find their 
way into the xylem as also does any water withdrawn from the proto- 
5—2 
