Notes on the Abso^ytion of Water by Aerial Organs of Plants. 431 
other one just touched the surface with the tips of the stellate hairs. The 
results of two experiments made in June on twigs from cultivated plants, 
no wild plants being available, are as follows : — 
I. Initial weight of A (touching the water) 0-036 
After 3 days 0-036 
Initial weight of B (just above the water) 0-051 
After 3 days 0-041 
Loss 0-010, equal to 20 per cent. 
II Initial weight of A 0-137 
After 3 days 0-132 
Loss 0*005, equal to 4 per cent. 
Initial weight of B 0-172 
After 3 days 0-139 
Loss 0-033, equal to 19 per cent. 
Thus in the one case the control specimen lost 20 per cent, of its 
weight by transpiration, and in the other case 19 per cent., while the 
leaves which were able to absorb water kept up their weight in the first 
experiment, and lost only 4 per cent, in the second one. 
This fully confirms my previous results, viz., that the stellate hairs of 
Mesembrianthemum densum are able to absorb water from the air, and 
that this amount is, under certain conditions, sufficient to replace the loss 
suffered by transpiration. 
The anatomical structure of these apical hairs is quite different from 
that of the ordinary water-storing epidermis-cells of the leaf. Each hair 
has an inflated basal part, which is inserted in a specially constructed cup. 
The walls of the hair itself are thick, but consist of cellulose with a very 
thin cuticula ; those of the cup-cells, especially on adult leaves, are highly 
culticularised. In the young leaf the sides of the cup only possess cells 
with thickened walls, while the bottom part of the hair is in immediate 
contact with a very delicate meristematic tissue. Below this are, at the 
circumference of the leaf, the assimilating cells, and in the centre the 
colourless water-storing mesophyll of the leaf. Later the tissue imme- 
diately below the base of the hair thickens and lignifies its walls, thus 
forming a barrier between the base of the hair and the water-tissue of 
the leaf, by which further communication between the two is rendered 
difficult and loss of water from the interior of the leaf prevented. It is 
obvious that the structure of these hairs is very elaborate and highly 
specialised, consequently they must possess some important function in 
the life of the plant. Their structure during the younger stages of the 
leaf is well adapted to the absorption of water, and as the experiments 
have shown that the leaves do absorb water, it seems clear that this was 
obtained through the hairs, and that the hairs are specially constructed 
