588 
Notes . 
In Helianthus multiflorus a cell from the same tissue measures very 
closely the same ; so that in these two instances we see that the walls 
of the cells of the palisade-parenchyma, so far as they are exposed 
to disruptive forces, are stressed far below the experimentally derived 
tenacity of cellulose. In fact there is a coefficient of safety amounting 
to 25. 
The dimensions of the cylindrical cells of the sheath are the 
following : — 
Cytisus Laburnum , length =• 100 mm., diameter =-030 mm. 
Helianthus multiflorus , length = • 108 mm., diameter =*o 18 mm. 
These are the maximum dimensions observed. The thickness of 
the walls in each case is about -ooi mm. 
It results from these figures that if the pressure is 300 grs. per 
sq. mm. that cell-walls of Cytisus Laburnum will be subject to a stress 
of less than 3,500 grs. per sq. mm. This leaves a coefficient of safety 
of at least 14. 
It has been noticed as probable that the walls of the cells of the 
spongy parenchyma do not, under normal circumstances, sustain any 
appreciable stress. But even if it is assumed that their cellulose 
membrane is sufficiently rigid to maintain its irregular shape when 
exposed to these high internal pressures, it is easily shown that the 
stress in the cell- walls does not rise above 1,500 or 2,000 grs. per 
sq. mm. 
So it appears that the wall of every cell of the leaf is amply strong 
to sustain the high osmotic pressures which are demonstrable as 
giving rigidity to the leaf, and that, so far as the strength of the cell- 
walls is concerned, much higher osmotic pressures than those actually 
observed might exist in the cells of the leaf. 
H. H. DIXON, Dublin. 
STRUCTURE OF CODIUM. — Two years ago, in the month 
of April, I gathered some material of C odium tomentosum near Ventry, 
Co. Kerry. In sections prepared from this for teaching purposes, 
I was struck by the peculiar appearance of the club-shaped ends 
of the ramifications of the coenocyte. Sections 10 fi thick, stained 
with Delafield’s Haematoxylin, showed in many of the branches of 
the coenocyte a stout axial strand of a violet substance. The strand 
is thin and more delicate in the narrow interweaving parts of the 
coenocyte, and thickens gradually as it passes out into the enlarged 
