NOTES. 
THE EFFECTS OF TROPICAL INSOLATION. — In my paper 
with this title, published in the September number of the Annals, 
I notice that, when speaking of the movements of the sensitive 
leaflets, I omitted to refer to Oltmann’s researches on this subject. 
Oltmann 1 was the first to show that in Robinia it is the pulvini which 
are directly stimulated to movement by a change in the intensity of 
the illumination. The observations I have made in Java and Ceylon 
are of interest as corroborating and extending the results obtained 
by Oltmann, and later by Macfarlane 2 , on this particular point. 
ALFRED J. EWART. 
Mason College, Birmingham. 
THE TENSILE STRENGTH OF CELL- WALLS.— Some time 
ago I estimated the osmotic pressure in the leaf-cells of several plants 
to range between 20-30 atmospheres (or 200-300 grs. per sq. mm.) 3 . 
It seemed to me of interest to ascertain what coefficient of safety 
was allowed by the plant to meet these high pressures. This may 
be done by determining the tenacity or tensile strength of cellulose, 
and estimating the stress in the cell-wall while the cell is distended by 
these pressures. 
The first was ascertained directly by weighing a single hair or fibre, 
detached from the surface of the seed of Gossypium , until it broke. 
From the breaking weight and the area of cross-section of the fibre, ’ 
its tenacity may be obtained. 
I applied the weight by slowly filling with water a light paper 
1 Oltmann, Flora, 1892, p. 234. 
2 Macfarlane, Bot. Centralblatt, 1895, I, p. 136. 
3 Notes from the Botanical School, Trinity College, Dublin, No. 2, May, 1897. 
[Annals of Botany, Vol. XI. No. XLIV. December, 1897.] 
