636 Thoday and Sykes.— Preliminary Observations on the 
of eosin, the plant stem firmly fixed by means of cotton wool in a hole 
bored in the cork, and the rest of the cylinder filled with water so that the 
branch was completely submerged. The eosin was observed to penetrate 
at rates considerably greater than those recorded by Hochreutiner, the 
maximum being 10 cm. in 4 \ hours. This suggested to us that experi- 
ments in situ might be interesting, for although the material was handled 
as carefully as possible it could not, from the nature of the method, be 
kept submerged during the short interval occupied in setting up the 
experiment. 
Experiments were therefore made with plants of P. lucens , growing in 
the river Cam, during July and August of this year. The method adopted 
was to attach a small glass bulb of eosin to the cut end of a submerged 
branch. A good leafy stem was chosen, cut under water, and left sub- 
merged for a short time. A little cotton wool was then wrapped round the 
stem near the cut end, a small bulb of eosin brought down to the surface of 
the water, and the cut end lifted for a moment above the surface and 
inserted in the bulb. When the experiment was of short duration the 
stem was merely held under water, but when a longer time was required it 
was attached at two or three points to a bamboo float and kept beneath the 
water by one or two small strips of lead bent round it. At the end of the 
experiment the bulb was removed and the stem at once examined. 
The rate of transmission of the eosin solution was found to be 
surprisingly rapid. The earlier experiments lasted from fifteen to five 
minutes, and in each case the eosin was found to have travelled up to the apex, 
a distance of 20 to 30 cm. The times of experiment were then reduced ; 
the appended table gives a number of the results so obtained for the rate 
of flow of the eosin. 
Time. 
Duration of 
experiment in 
minutes. 
Number of 
internodes traversed 
by eosin. 
Total length 
traversed by 
eosin, in cm. 
Rate of flow 
in centimetres 
per minute. 
8.15 p.m. 
1 
H 
5-7 
5-7 
8.28 p.m. 
1 
1 
7*5 
7-5 
11.0 a.m. 
2 
4 
19.0 
9-5 
7.53 p.m. 
2 
2-2 
14-0 
7.0 
4.52 p.m. 
3 
7 
17-5 
5.8 
12.23 p.m. 
3 
4 
18.2 
6-i 
The results are found to depend largely on the state of the material 
employed, and such high results as those given in the table were only 
obtained with healthy branches. Probably external conditions also affect 
the results ; this point we hope to investigate later. It was not found that 
the length of time which elapsed between the cutting of the stem and the 
immersion of its cut end in eosin had any appreciable effect on the result of 
the experiment. 
