Notes . 569 
correspond to optimal solutions, in which the cells live longer than 
in any other. 
The investigations just alluded to have proved that de Vries’ 
constant isotonic coefficients , excellent as they are for a first approxima- 
tion, are not sufficiently exact for more minute experiments. Here 
it is advisable to use, instead of them, the coefficients of electric con- 
ductivity, which vary slightly with the concentration of the solution. 
Thus, osmotic pressures are not strictly proportional to the con- 
centration of the plasmolysing solutions, and these pressures ought 
no more to be expressed in molecule-grams of NO s K, as is now 
generally done. The use of an atmosphere as unit, though better, is 
also objectionable, as it varies from one place to another. 
I would therefore suggest to adopt the C.G.S. unit of pressure, 
viz. 1 dyne per sq. cm., or rather (to avoid useless decimals) 
1 myriadyne per sq. cm ., i. e. the pressure of 10,000 dynes per sq. cm., 
the dyne being the force which gives the mass of 1 gram in 1 second 
an acceleration of 1 cm. per second. 
This unit is roughly equal to T J<y atmosphere ; we found it to be 
very convenient for all sorts of osmotic calculations. 
L. ERRERA, Brussels. 
THE FORM OF THE PROTOPLASMIC BODY IN CERTAIN 
FLORIDEAE. — In Ceramium ruhrum and other species a strong 
strand of protoplasm runs along the axial cells from pit to pit. In 
this strand the nucleus is occasionally suspended ; more often it lies 
over the pit at the base of the strand. 
In Dasya coccinea the branches of limited growth run out into 
pointed uncorticated filaments, the cells of which are large. Across 
the vacuole of these cells, running from pit to pit, occurs a thread 
of protoplasm much more delicate than the corresponding structure 
in Ceramium. 
In Callithamnion byssoides threads of protoplasm radiate from 
a cushion lying over the pit and end blindly on the vacuole. 
These threads are in incessant movement, swinging over, bending 
on themselves, and extending or retracting. All these phenomena 
point to the great physiological importance of the pit-communication 
between cell and cell. 
University College, Bangor. 
Q q 2 
R. W. PHILLIPS. 
